ipsin
Level 9
Solved 243 out of 384
Problems Solved
1Problem 1 (solved by 214054) "Add all the natural numbers below one thousand that are multiples of 3 or 5." | 2Problem 2 (solved by 176888) "By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms." | 3Problem 3 (solved by 128666) "Find the largest prime factor of a composite number." | 4Problem 4 (solved by 118574) "Find the largest palindrome made from the product of two 3-digit numbers." | 5Problem 5 (solved by 132023) "What is the smallest number divisible by each of the numbers 1 to 20?" | 6Problem 6 (solved by 133621) "What is the difference between the sum of the squares and the square of the sums?" | 7Problem 7 (solved by 113043) "Find the 10001st prime." | 8Problem 8 (solved by 99918) "Discover the largest product of five consecutive digits in the 1000-digit number." | 9Problem 9 (solved by 100000) "Find the only Pythagorean triplet, {a, b, c}, for which a + b + c = 1000." | 10Problem 10 (solved by 90966) "Calculate the sum of all the primes below two million." | 11Problem 11 (solved by 68851) "What is the greatest product of four adjacent numbers on the same straight line in the 20 by 20 grid?" | 12Problem 12 (solved by 60931) "What is the value of the first triangle number to have over five hundred divisors?" | 13Problem 13 (solved by 67490) "Find the first ten digits of the sum of one-hundred 50-digit numbers." | 14Problem 14 (solved by 65490) "Find the longest sequence using a starting number under one million." | 15Problem 15 (solved by 53857) "Starting in the top left corner in a 20 by 20 grid, how many routes are there to the bottom right corner?" | 16Problem 16 (solved by 71511) "What is the sum of the digits of the number 21000?" | 17Problem 17 (solved by 45176) "How many letters would be needed to write all the numbers in words from 1 to 1000?" | 18Problem 18 (solved by 45602) "Find the maximum sum travelling from the top of the triangle to the base." | 19Problem 19 (solved by 41553) "How many Sundays fell on the first of the month during the twentieth century?" | 20Problem 20 (solved by 68309) "Find the sum of digits in 100!" | 21Problem 21 (solved by 45172) "Evaluate the sum of all amicable pairs under 10000." | 22Problem 22 (solved by 42316) "What is the total of all the name scores in the file of first names?" | 23Problem 23 (solved by 30898) "Find the sum of all the positive integers which cannot be written as the sum of two abundant numbers." | 24Problem 24 (solved by 37010) "What is the millionth lexicographic permutation of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9?" | 25Problem 25 (solved by 50698) "What is the first term in the Fibonacci sequence to contain 1000 digits?" |
26Problem 26 (solved by 25797) "Find the value of d < 1000 for which 1/d contains the longest recurring cycle." | 27Problem 27 (solved by 27314) "Find a quadratic formula that produces the maximum number of primes for consecutive values of n." | 28Problem 28 (solved by 39030) "What is the sum of both diagonals in a 1001 by 1001 spiral?" | 29Problem 29 (solved by 33511) "How many distinct terms are in the sequence generated by ab for 2 ≤ a ≤ 100 and 2 ≤ b ≤ 100?" | 30Problem 30 (solved by 36138) "Find the sum of all the numbers that can be written as the sum of fifth powers of their digits." | 31Problem 31 (solved by 25167) "Investigating combinations of English currency denominations." | 32Problem 32 (solved by 22043) "Find the sum of all numbers that can be written as pandigital products." | 33Problem 33 (solved by 23545) "Discover all the fractions with an unorthodox cancelling method." | 34Problem 34 (solved by 31817) "Find the sum of all numbers which are equal to the sum of the factorial of their digits." | 35Problem 35 (solved by 29015) "How many circular primes are there below one million?" | 36Problem 36 (solved by 31687) "Find the sum of all numbers less than one million, which are palindromic in base 10 and base 2." | 37Problem 37 (solved by 24085) "Find the sum of all eleven primes that are both truncatable from left to right and right to left." | 38Problem 38 (solved by 20189) "What is the largest 1 to 9 pandigital that can be formed by multiplying a fixed number by 1, 2, 3, ... ?" | 39Problem 39 (solved by 23748) "If p is the perimeter of a right angle triangle, {a, b, c}, which value, for p ≤ 1000, has the most solutions?" | 40Problem 40 (solved by 27110) "Finding the nth digit of the fractional part of the irrational number." | 41Problem 41 (solved by 22279) "What is the largest n-digit pandigital prime that exists?" | 42Problem 42 (solved by 26574) "How many triangle words does the list of common English words contain?" | 43Problem 43 (solved by 18205) "Find the sum of all pandigital numbers with an unusual sub-string divisibility property." | 44Problem 44 (solved by 17640) "Find the smallest pair of pentagonal numbers whose sum and difference is pentagonal." | 45Problem 45 (solved by 25362) "After 40755, what is the next triangle number that is also pentagonal and hexagonal?" | 46Problem 46 (solved by 18553) "What is the smallest odd composite that cannot be written as the sum of a prime and twice a square?" | 47Problem 47 (solved by 18516) "Find the first four consecutive integers to have four distinct primes factors." | 48Problem 48 (solved by 44315) "Find the last ten digits of 11 + 22 + ... + 10001000." | 49Problem 49 (solved by 17854) "Find arithmetic sequences, made of prime terms, whose four digits are permutations of each other." | 50Problem 50 (solved by 19347) "Which prime, below one-million, can be written as the sum of the most consecutive primes?" |
51Problem 51 (solved by 9975) "Find the smallest prime which, by changing the same part of the number, can form eight different primes." | 52Problem 52 (solved by 24473) "Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits in some order." | 53Problem 53 (solved by 22218) "How many values of C(n,r), for 1 ≤ n ≤ 100, exceed one-million?" | 54Problem 54 (solved by 11303) "How many hands did player one win in the game of poker?" | 55Problem 55 (solved by 19677) "How many Lychrel numbers are there below ten-thousand?" | 56Problem 56 (solved by 20908) "Considering natural numbers of the form, ab, finding the maximum digital sum." | 57Problem 57 (solved by 13779) "Investigate the expansion of the continued fraction for the square root of two." | 58Problem 58 (solved by 13339) "Investigate the number of primes that lie on the diagonals of the spiral grid." | 59Problem 59 (solved by 14739) "Using a brute force attack, can you decrypt the cipher using XOR encryption?" | 60Problem 60 (solved by 7985) "Find a set of five primes for which any two primes concatenate to produce another prime." | 61Problem 61 (solved by 8140) "Find the sum of the only set of six 4-digit figurate numbers with a cyclic property." | 62Problem 62 (solved by 10116) "Find the smallest cube for which exactly five permutations of its digits are cube." | 63Problem 63 (solved by 15295) "How many n-digit positive integers exist which are also an nth power?" | 64Problem 64 (solved by 7111) "How many continued fractions for N ≤ 10000 have an odd period?" | 65Problem 65 (solved by 9578) "Find the sum of digits in the numerator of the 100th convergent of the continued fraction for e." | 66Problem 66 (solved by 6406) "Investigate the Diophantine equation x2 − Dy2 = 1." | 67Problem 67 (solved by 34073) "Using an efficient algorithm find the maximal sum in the triangle?" | 68Problem 68 (solved by 6669) "What is the maximum 16-digit string for a "magic" 5-gon ring?" | 69Problem 69 (solved by 12281) "Find the value of n ≤ 1,000,000 for which n/φ(n) is a maximum." | 70Problem 70 (solved by 7678) "Investigate values of n for which φ(n) is a permutation of n." | 71Problem 71 (solved by 10426) "Listing reduced proper fractions in ascending order of size." | 72Problem 72 (solved by 7685) "How many elements would be contained in the set of reduced proper fractions for d ≤ 1,000,000?" | 73Problem 73 (solved by 9540) "How many fractions lie between 1/3 and 1/2 in a sorted set of reduced proper fractions?" | 74Problem 74 (solved by 9242) "Determine the number of factorial chains that contain exactly sixty non-repeating terms." | 75Problem 75 (solved by 5836) "Find the number of different lengths of wire that can form a right angle triangle in only one way." |
76Problem 76 (solved by 10363) "How many different ways can one hundred be written as a sum of at least two positive integers?" | 77Problem 77 (solved by 6086) "What is the first value which can be written as the sum of primes in over five thousand different ways?" | 78Problem 78 (solved by 5342) "Investigating the number of ways in which coins can be separated into piles." | 79Problem 79 (solved by 18682) "By analysing a user's login attempts, can you determine the secret numeric passcode?" | 80Problem 80 (solved by 6809) "Calculating the digital sum of the decimal digits of irrational square roots." | 81Problem 81 (solved by 11815) "Find the minimal path sum from the top left to the bottom right by moving right and down." | 82Problem 82 (solved by 7195) "Find the minimal path sum from the left column to the right column." | 83Problem 83 (solved by 5974) "Find the minimal path sum from the top left to the bottom right by moving left, right, up, and down." | 84Problem 84 (solved by 4030) "In the game, Monopoly, find the three most popular squares when using two 4-sided dice." | 85Problem 85 (solved by 8883) "Investigating the number of rectangles in a rectangular grid." | 86Problem 86 (solved by 4088) "Exploring the shortest path from one corner of a cuboid to another." | 87Problem 87 (solved by 7182) "Investigating numbers that can be expressed as the sum of a prime square, cube, and fourth power?" | 88Problem 88 (solved by 2856) "Exploring minimal product-sum numbers for sets of different sizes." | 89Problem 89 (solved by 6949) "Develop a method to express Roman numerals in minimal form." | 90Problem 90 (solved by 3460) "An unexpected way of using two cubes to make a square." | 91Problem 91 (solved by 5347) "Find the number of right angle triangles in the quadrant." | 92Problem 92 (solved by 14316) "Investigating a square digits number chain with a surprising property." | 93Problem 93 (solved by 3667) "Using four distinct digits and the rules of arithmetic, find the longest sequence of target numbers." | 94Problem 94 (solved by 3897) "Investigating almost equilateral triangles with integral sides and area." | 95Problem 95 (solved by 4637) "Find the smallest member of the longest amicable chain with no element exceeding one million." | 96Problem 96 (solved by 5824) "Devise an algorithm for solving Su Doku puzzles." | 97Problem 97 (solved by 20111) "Find the last ten digits of the non-Mersenne prime: 28433 × 27830457 + 1." | 98Problem 98 (solved by 3467) "Investigating words, and their anagrams, which can represent square numbers." | 99Problem 99 (solved by 11381) "Which base/exponent pair in the file has the greatest numerical value?" | 100Problem 100 (solved by 5080) "Finding the number of blue discs for which there is 50% chance of taking two blue." |
101Problem 101 (solved by 3534) "Investigate the optimum polynomial function to model the first k terms of a given sequence." | 102Problem 102 (solved by 8096) "For how many triangles in the text file does the interior contain the origin?" | 103Problem 103 (solved by 2633) "Investigating sets with a special subset sum property." | 104Problem 104 (solved by 6024) "Finding Fibonacci numbers for which the first and last nine digits are pandigital." | 105Problem 105 (solved by 2657) "Find the sum of the special sum sets in the file." | 106Problem 106 (solved by 2124) "Find the minimum number of comparisons needed to identify special sum sets." | 107Problem 107 (solved by 3815) "Determining the most efficient way to connect the network." | 108Problem 108 (solved by 5050) "Solving the Diophantine equation 1/x + 1/y = 1/n." | 109Problem 109 (solved by 2675) "How many distinct ways can a player checkout in the game of darts with a score of less than 100?" | 110Problem 110 (solved by 3142) "Find an efficient algorithm to analyse the number of solutions of the equation 1/x + 1/y = 1/n." | 111Problem 111 (solved by 2533) "Search for 10-digit primes containing the maximum number of repeated digits." | 112Problem 112 (solved by 9107) "Investigating the density of "bouncy" numbers." | 113Problem 113 (solved by 4314) "How many numbers below a googol (10100) are not "bouncy"?" | 114Problem 114 (solved by 3859) "Investigating the number of ways to fill a row with separated blocks that are at least three units long." | 115Problem 115 (solved by 3535) "Finding a generalisation for the number of ways to fill a row with separated blocks." | 116Problem 116 (solved by 4283) "Investigating the number of ways of replacing square tiles with one of three coloured tiles." | 117Problem 117 (solved by 3952) "Investigating the number of ways of tiling a row using different-sized tiles." | 118Problem 118 (solved by 2288) "Exploring the number of ways in which sets containing prime elements can be made." | 119Problem 119 (solved by 4346) "Investigating the numbers which are equal to sum of their digits raised to some power." | 120Problem 120 (solved by 5285) "Finding the maximum remainder when (a − 1)n + (a + 1)n is divided by a2." | 121Problem 121 (solved by 3325) "Investigate the game of chance involving coloured discs." | 122Problem 122 (solved by 2786) "Finding the most efficient exponentiation method." | 123Problem 123 (solved by 4503) "Determining the remainder when (pn − 1)n + (pn + 1)n is divided by pn2." | 124Problem 124 (solved by 5700) "Determining the kth element of the sorted radical function." | 125Problem 125 (solved by 5311) "Finding square sums that are palindromic." |
126Problem 126 (solved by 1543) "Exploring the number of cubes required to cover every visible face on a cuboid." | 127Problem 127 (solved by 2053) "Investigating the number of abc-hits below a given limit." | 128Problem 128 (solved by 1681) "Which tiles in the hexagonal arrangement have prime differences with neighbours?" | 129Problem 129 (solved by 2286) "Investigating minimal repunits that divide by n." | 130Problem 130 (solved by 2171) "Finding composite values, n, for which n−1 is divisible by the length of the smallest repunits that divide it." | 131Problem 131 (solved by 2765) "Determining primes, p, for which n3 + n2p is a perfect cube." | 132Problem 132 (solved by 2424) "Determining the first forty prime factors of a very large repunit." | 133Problem 133 (solved by 2084) "Investigating which primes will never divide a repunit containing 10n digits." | 134Problem 134 (solved by 2514) "Finding the smallest positive integer related to any pair of consecutive primes." | 135Problem 135 (solved by 2298) "Determining the number of solutions of the equation x2 − y2 − z2 = n." | 136Problem 136 (solved by 2043) "Discover when the equation x2 − y2 − z2 = n has a unique solution." | 137Problem 137 (solved by 1967) "Determining the value of infinite polynomial series for which the coefficients are Fibonacci numbers." | 138Problem 138 (solved by 2199) "Investigating isosceles triangle for which the height and base length differ by one." | 139Problem 139 (solved by 1973) "Finding Pythagorean triangles which allow the square on the hypotenuse to be tiled." | 140Problem 140 (solved by 1541) "Investigating the value of infinite polynomial series for which the coefficients are a linear second order recurrence relation." | 141Problem 141 (solved by 1313) "Investigating progressive numbers, n, which are also square." | 142Problem 142 (solved by 2181) "Perfect Square Collection" | 143Problem 143 (solved by 966) "Investigating the Torricelli point of a triangle " | 144Problem 144 (solved by 1817) "Investigating multiple reflections of a laser beam. " | 145Problem 145 (solved by 6446) "How many reversible numbers are there below one-billion?" | 146Problem 146 (solved by 1861) "Investigating a Prime Pattern " | 147Problem 147 (solved by 1070) "Rectangles in cross-hatched grids" | 148Problem 148 (solved by 1994) "Exploring Pascal's triangle." | 149Problem 149 (solved by 1771) "Searching for a maximum-sum subsequence." | 150Problem 150 (solved by 1427) "Searching a triangular array for a sub-triangle having minimum-sum." |
151Problem 151 (solved by 1956) "Paper sheets of standard sizes: an expected-value problem." | 152Problem 152 (solved by 998) "Writing 1/2 as a sum of inverse squares" | 153Problem 153 (solved by 942) "Investigating Gaussian Integers" | 154Problem 154 (solved by 993) "Exploring Pascal's pyramid." | 155Problem 155 (solved by 1355) "Counting Capacitor Circuits." | 156Problem 156 (solved by 890) "Counting Digits" | 157Problem 157 (solved by 1013) "Solving the diophantine equation 1/a+1/b= p/10n " | 158Problem 158 (solved by 1419) "Exploring strings for which only one character comes lexicographically after its neighbour to the left." | 159Problem 159 (solved by 1284) "Digital root sums of factorisations. " | 160Problem 160 (solved by 1259) "Factorial trailing digits" | 161Problem 161 (solved by 805) "Triominoes" | 162Problem 162 (solved by 2252) "Hexadecimal numbers" | 163Problem 163 (solved by 742) "Cross-hatched triangles" | 164Problem 164 (solved by 2319) "Numbers for which no three consecutive digits have a sum greater than a given value." | 165Problem 165 (solved by 1019) "Intersections" | 166Problem 166 (solved by 1611) "Criss Cross" | 167Problem 167 (solved by 688) "Investigating Ulam sequences" | 168Problem 168 (solved by 1064) "Number Rotations" | 169Problem 169 (solved by 1654) "Exploring the number of different ways a number can be expressed as a sum of powers of 2. " | 170Problem 170 (solved by 793) "Find the largest 0 to 9 pandigital that can be formed by concatenating products." | 171Problem 171 (solved by 971) "Finding numbers for which the sum of the squares of the digits is a square." | 172Problem 172 (solved by 1503) "Investigating numbers with few repeated digits." | 173Problem 173 (solved by 3774) "Using up to one million tiles how many different "hollow" square laminae can be formed?" | 174Problem 174 (solved by 2515) "Counting the number of "hollow" square laminae that can form one, two, three, ... distinct arrangements." | 175Problem 175 (solved by 773) "Fractions involving the number of different ways a number can be expressed as a sum of powers of 2. " |
176Problem 176 (solved by 821) "Rectangular triangles that share a cathetus." | 177Problem 177 (solved by 555) "Integer angled Quadrilaterals." | 178Problem 178 (solved by 1392) "Step Numbers" | 179Problem 179 (solved by 4755) "Consecutive positive divisors " | 180Problem 180 (solved by 665) "Rational zeros of a function of three variables." | 181Problem 181 (solved by 760) "Investigating in how many ways objects of two different colours can be grouped." | 182Problem 182 (solved by 1061) "RSA encryption" | 183Problem 183 (solved by 2096) "Maximum product of parts" | 184Problem 184 (solved by 654) "Triangles containing the origin." | 185Problem 185 (solved by 1282) "Number Mind" | 186Problem 186 (solved by 1131) "Connectedness of a network." | 187Problem 187 (solved by 4628) "Semiprimes" | 188Problem 188 (solved by 2847) "The hyperexponentiation of a number" | 189Problem 189 (solved by 811) "Tri-colouring a triangular grid" | 190Problem 190 (solved by 1703) "Maximising a weighted product " | 191Problem 191 (solved by 2954) "Prize Strings" | 192Problem 192 (solved by 674) "Best Approximations" | 193Problem 193 (solved by 1258) "Squarefree Numbers" | 194Problem 194 (solved by 594) "Coloured Configurations" | 195Problem 195 (solved by 568) "Inscribed circles of triangles with one angle of 60 degrees" | 196Problem 196 (solved by 926) "Prime triplets" | 197Problem 197 (solved by 2261) "Investigating the behaviour of a recursively defined sequence" | 198Problem 198 (solved by 480) "Ambiguous Numbers" | 199Problem 199 (solved by 776) "Iterative Circle Packing" | 200Problem 200 (solved by 909) "Find the 200th prime-proof sqube containing the contiguous sub-string "200"" |
201Problem 201 (solved by 920) "Subsets with a unique sum" | 202Problem 202 (solved by 1093) "Laserbeam" | 203Problem 203 (solved by 3977) "Squarefree Binomial Coefficients" | 204Problem 204 (solved by 3275) "Generalised Hamming Numbers" | 205Problem 205 (solved by 6266) "Dice Game" | 206Problem 206 (solved by 9011) "Concealed Square" | 207Problem 207 (solved by 2193) "Integer partition equations" | 208Problem 208 (solved by 771) "Robot Walks" | 209Problem 209 (solved by 1147) "Circular Logic" | 210Problem 210 (solved by 751) "Obtuse Angled Triangles" | 211Problem 211 (solved by 1601) "Divisor Square Sum" | 212Problem 212 (solved by 680) "Combined Volume of Cuboids" | 213Problem 213 (solved by 987) "Flea Circus" | 214Problem 214 (solved by 2288) "Totient Chains" | 215Problem 215 (solved by 1683) "Crack-free Walls" | 216Problem 216 (solved by 1754) "Investigating the primality of numbers of the form 2n2-1" | 217Problem 217 (solved by 684) "Balanced Numbers" | 218Problem 218 (solved by 1294) "Perfect right-angled triangles" | 219Problem 219 (solved by 712) "Skew-cost coding" | 220Problem 220 (solved by 1204) "Heighway Dragon" | 221Problem 221 (solved by 927) "Alexandrian Integers" | 222Problem 222 (solved by 988) "Sphere Packing" | 223Problem 223 (solved by 632) "Almost right-angled triangles I" | 224Problem 224 (solved by 544) "Almost right-angled triangles II" | 225Problem 225 (solved by 1904) "Tribonacci non-divisors" |
226Problem 226 (solved by 868) "A Scoop of Blancmange" | 227Problem 227 (solved by 890) "The Chase" | 228Problem 228 (solved by 691) "Minkowski Sums" | 229Problem 229 (solved by 667) "Four Representations using Squares" | 230Problem 230 (solved by 1433) "Fibonacci Words" | 231Problem 231 (solved by 2454) "The prime factorisation of binomial coefficients" | 232Problem 232 (solved by 804) "The Race" | 233Problem 233 (solved by 681) "Lattice points on a circle" | 234Problem 234 (solved by 1638) "Semidivisible numbers" | 235Problem 235 (solved by 2482) "An Arithmetic Geometric sequence" | 236Problem 236 (solved by 483) "Luxury Hampers" | 237Problem 237 (solved by 708) "Tours on a 4 x n playing board" | 238Problem 238 (solved by 506) "Infinite string tour" | 239Problem 239 (solved by 841) "Twenty-two Foolish Primes" | 240Problem 240 (solved by 1026) "Top Dice" | 241Problem 241 (solved by 457) "Perfection Quotients" | 242Problem 242 (solved by 526) "Odd Triplets" | 243Problem 243 (solved by 2432) "Resilience" | 244Problem 244 (solved by 636) "Sliders" | 245Problem 245 (solved by 421) "Coresilience" | 246Problem 246 (solved by 426) "Tangents to an ellipse" | 247Problem 247 (solved by 739) "Squares under a hyperbola" | 248Problem 248 (solved by 595) "Numbers for which Euler’s totient function equals 13!" | 249Problem 249 (solved by 1012) "Prime Subset Sums" | 250Problem 250 (solved by 1144) "250250" |
251Problem 251 (solved by 617) "Cardano Triplets" | 252Problem 252 (solved by 475) "Convex Holes" | 253Problem 253 (solved by 468) "Tidying up" | 254Problem 254 (solved by 491) "Sums of Digit Factorials" | 255Problem 255 (solved by 465) "Rounded Square Roots" | 256Problem 256 (solved by 389) "Tatami-Free Rooms" | 257Problem 257 (solved by 359) "Angular Bisectors" | 258Problem 258 (solved by 656) "A lagged Fibonacci sequence" | 259Problem 259 (solved by 652) "Reachable Numbers" | 260Problem 260 (solved by 628) "Stone Game" | 261Problem 261 (solved by 360) "Pivotal Square Sums" | 262Problem 262 (solved by 399) "Mountain Range." | 263Problem 263 (solved by 512) "An engineers' dream come true" | 264Problem 264 (solved by 345) "Triangle Centres" | 265Problem 265 (solved by 1832) "Binary Circles" | 266Problem 266 (solved by 699) "Pseudo Square Root" | 267Problem 267 (solved by 1305) "Billionaire" | 268Problem 268 (solved by 630) "Counting numbers with at least four distinct prime factors less than 100" | 269Problem 269 (solved by 363) "Polynomials with at least one integer root" | 270Problem 270 (solved by 370) "Cutting Squares" | 271Problem 271 (solved by 907) "Modular Cubes, part 1" | 272Problem 272 (solved by 409) "Modular Cubes, part 2" | 273Problem 273 (solved by 607) "Sum of Squares" | 274Problem 274 (solved by 698) "Divisibility Multipliers" | 275Problem 275 (solved by 344) "Balanced Sculptures" |
276Problem 276 (solved by 481) "Primitive Triangles" | 277Problem 277 (solved by 1335) "A Modified Collatz sequence" | 278Problem 278 (solved by 462) "Linear Combinations of Semiprimes" | 279Problem 279 (solved by 353) "Triangles with integral sides and an integral angle " | 280Problem 280 (solved by 470) "Ant and seeds" | 281Problem 281 (solved by 425) "Pizza Toppings" | 282Problem 282 (solved by 465) "The Ackermann function" | 283Problem 283 (solved by 369) "Integer sided triangles for which the area/perimeter ratio is integral." | 284Problem 284 (solved by 595) "Steady Squares" | 285Problem 285 (solved by 537) "Pythagorean odds" | 286Problem 286 (solved by 839) "Scoring probabilities" | 287Problem 287 (solved by 650) "Quadtree encoding (a simple compression algorithm)" | 288Problem 288 (solved by 546) "An enormous factorial" | 289Problem 289 (solved by 293) "Eulerian Cycles" | 290Problem 290 (solved by 478) "Digital Signature" | 291Problem 291 (solved by 571) "Panaitopol Primes" | 292Problem 292 (solved by 331) "Pythagorean Polygons" | 293Problem 293 (solved by 1002) "Pseudo-Fortunate Numbers" | 294Problem 294 (solved by 420) "Sum of digits - experience #23" | 295Problem 295 (solved by 297) "Lenticular holes" | 296Problem 296 (solved by 323) "Angular Bisector and Tangent" | 297Problem 297 (solved by 1175) "Zeckendorf Representation" | 298Problem 298 (solved by 358) "Selective Amnesia" | 299Problem 299 (solved by 358) "Three similar triangles" | 300Problem 300 (solved by 455) "Protein folding" |
301Problem 301 (solved by 1894) "Nim" | 302Problem 302 (solved by 348) "Strong Achilles Numbers" | 303Problem 303 (solved by 1388) "Multiples with small digits" | 304Problem 304 (solved by 778) "Primonacci" | 305Problem 305 (solved by 340) "Reflexive Position" | 306Problem 306 (solved by 495) "Paper-strip Game" | 307Problem 307 (solved by 636) "Chip Defects" | 308Problem 308 (solved by 382) "An amazing Prime-generating Automaton" | 309Problem 309 (solved by 359) "Integer Ladders" | 310Problem 310 (solved by 425) "Nim Square" | 311Problem 311 (solved by 249) "Biclinic Integral Quadrilaterals" | 312Problem 312 (solved by 377) "Cyclic paths on Sierpiński graphs " | 313Problem 313 (solved by 534) "Sliding game" | 314Problem 314 (solved by 263) "The Mouse on the Moon" | 315Problem 315 (solved by 947) "Digital root clocks" | 316Problem 316 (solved by 314) "Numbers in decimal expansions" | 317Problem 317 (solved by 864) "Firecracker" | 318Problem 318 (solved by 371) "2011 nines" | 319Problem 319 (solved by 213) "Bounded Sequences" | 320Problem 320 (solved by 333) "Factorials divisible by a huge integer" | 321Problem 321 (solved by 637) "Swapping Counters" | 322Problem 322 (solved by 233) "Binomial coefficients divisible by 10" | 323Problem 323 (solved by 1031) "Bitwise-OR operations on random integers" | 324Problem 324 (solved by 293) "Building a tower" | 325Problem 325 (solved by 251) "Stone Game II" |
326Problem 326 (solved by 260) "Modulo Summations" | 327Problem 327 (solved by 477) "Rooms of Doom" | 328Problem 328 (solved by 212) "Lowest-cost Search" | 329Problem 329 (solved by 743) "Prime Frog" | 330Problem 330 (solved by 244) "Euler's Number" | 331Problem 331 (solved by 186) "Cross flips" | 332Problem 332 (solved by 289) "Spherical triangles" | 333Problem 333 (solved by 415) "Special partitions" | 334Problem 334 (solved by 234) "Spilling the beans" | 335Problem 335 (solved by 229) "Gathering the beans" | 336Problem 336 (solved by 582) "Maximix Arrangements" | 337Problem 337 (solved by 234) "Totient Stairstep Sequences" | 338Problem 338 (solved by 176) "Cutting Rectangular Grid Paper" | 339Problem 339 (solved by 253) "Peredur fab Efrawg" | 340Problem 340 (solved by 368) "Crazy Function" | 341Problem 341 (solved by 396) "Golomb's self-describing sequence" | 342Problem 342 (solved by 338) "The totient of a square is a cube" | 343Problem 343 (solved by 590) "Fractional Sequences" | 344Problem 344 (solved by 116) "Silver dollar game" | 345Problem 345 (solved by 1091) "Matrix Sum" | 346Problem 346 (solved by 822) "Strong Repunits" | 347Problem 347 (solved by 808) "Largest integer divisible by two primes" | 348Problem 348 (solved by 723) "Sum of a square and a cube" | 349Problem 349 (solved by 625) "Langton's ant" | 350Problem 350 (solved by 194) "Constraining the least greatest and the greatest least" |
351Problem 351 (solved by 738) "Hexagonal orchards" | 352Problem 352 (solved by 239) "Blood tests" | 353Problem 353 (solved by 203) "Risky moon" | 354Problem 354 (solved by 140) "Distances in a bee's honeycomb " | 355Problem 355 (solved by 238) "Maximal coprime subset" | 356Problem 356 (solved by 225) "Largest roots of cubic polynomials" | 357Problem 357 (solved by 1295) "Prime generating integers" | 358Problem 358 (solved by 516) "Cyclic numbers" | 359Problem 359 (solved by 477) "Hilbert's New Hotel" | 360Problem 360 (solved by 298) "Scary Sphere" | 361Problem 361 (solved by 103) "Subsequence of Thue-Morse sequence" | 362Problem 362 (solved by 195) "Squarefree factors" | 363Problem 363 (solved by 382) "Bézier Curves" | 364Problem 364 (solved by 273) "Comfortable distance" | 365Problem 365 (solved by 353) "A huge binomial coefficient" | 366Problem 366 (solved by 243) "Stone Game III" | 367Problem 367 (solved by 163) "bozo sort" | 368Problem 368 (solved by 246) "A Kempner-like series" | 369Problem 369 (solved by 215) "Badugi " | 370Problem 370 (solved by 225) "Geometric triangles " | 371Problem 371 (solved by 399) "Licence plates" | 372Problem 372 (solved by 194) "Pencils of rays" | 373Problem 373 (solved by 167) "Circumscribed Circles" | 374Problem 374 (solved by 244) "Maximum Integer Partition Product " | 375Problem 375 (solved by 279) "Minimum of subsequences" |
376Problem 376 (solved by 102) "Nontransitive sets of dice" | 377Problem 377 (solved by 216) "Sum of digits, experience 13" | 378Problem 378 (solved by 232) "Triangle Triples" | 379Problem 379 (solved by 133) "Least common multiple count" | 380Problem 380 (solved by 129) "Amazing Mazes!" | 381Problem 381 (solved by 554) "(prime-k) factorial" | 382Problem 382 (solved by 99) "Generating polygons" | 383Problem 383 (solved by 115) "Divisibility comparison between factorials" | 384Problem 384 (solved by 42) "Rudin-Shapiro sequence" |
Levels Completed
 |  |  |  |  |  |  |  | | 250 |
275 | 300 | 325 | 350 |
Awards Earned
 Decathlete Solve ten consecutive problems |  Centurion Solve one hundred consecutive problems |  As Easy As Pi Solve problems 3, 14, 15, 92, 65, 35, 89, 79, 32, 38, and 46 |  One In A Hundred Be among the first hundred to solve a problem |  Unlucky Squares Solve thirteen square numbered problems |  Prime Obsession Solve fifty prime numbered problems |  Baby Steps Solve three problems |  The Journey Begins Progress to Level 1 by solving twenty-five problems | Perfection Perfection Solve every problem |  Daring Dozen Solve twelve problems with an ID containing three digits |
 On The Ball Solve the most recent problem | On The Ball II On The Ball II Solve the five most recent problems | State Of The Art State Of The Art Solve the most recent twenty-five problems | Trinary Triumph Trinary Triumph Solve problems 1, 3, 9, 27, 81, and 243 |  Fibonacci Fever Solve the first twelve Fibonacci numbered problems | Triangle Trophy Triangle Trophy Solve the first twenty-five triangle numbered problems | Lucky Luke Lucky Luke Solve fifty lucky numbered problems | High Flyer High Flyer Progress to the maximum level | Gold Medal Gold Medal The first to solve a problem |  Pythagorean Triplet Solve three Pythagorean problems |
 Déjà Vu Solve ten pairs of related problems |