These are solutions to the problems listed on Project Euler.
WARNING - Do not peek at any of these pages if you want to enjoy the benefits of Project Euler, unless you have already solved the problems.
From the website:
I learned so much solving problem XXX so is it okay to publish my solution elsewhere?
It appears that you have answered your own question. There is nothing quite like that “Aha!” moment when you finally beat a problem which you have been working on for some time. It is often through the best of intentions in wishing to share our insights so that others can enjoy that moment too. Sadly, however, that will not be the case for your readers. Real learning is an active process and seeing how it is done is a long way from experiencing that epiphany of discovery. Please do not deny others what you have so richly valued yourself.
Problem titles (up to 100)
1 Multiples of 3 and 5 .05 2 Even Fibonacci numbers .05 3 Largest prime factor .05 4 Largest palindrome product .05 5 Smallest multiple .05 6 Sum square difference .05 7 10001st prime .05 8 Largest product in a series .05 9 Special Pythagorean triplet .05 10 Summation of primes .05 11 Largest product in a grid .05 12 Highly divisible triangular number .05 13 Large sum .05 14 Longest Collatz sequence .05 15 Lattice paths .05 16 Power digit sum .05 17 Number letter counts .05 18 Maximum path sum I .05 19 Counting Sundays .05 20 Factorial digit sum .05 21 Amicable numbers .05 22 Names scores .05 23 Non-abundant sums .05 24 Lexicographic permutations .05 25 1000-digit Fibonacci number .05 26 Reciprocal cycles .05 27 Quadratic primes .05 28 Number spiral diagonals .05 29 Distinct powers .05 30 Digit fifth powers .05 31 Coin sums .05 32 Pandigital products .05 33 Digit cancelling fractions .05 34 Digit factorials .05 35 Circular primes .05 36 Double-base palindromes .05 37 Truncatable primes .05 38 Pandigital multiples .05 39 Integer right triangles .05 40 Champernowne's constant .05 41 Pandigital prime .05 42 Coded triangle numbers .05 43 Sub-string divisibility .05 44 Pentagon numbers .05 45 Triangular, pentagonal, and hexagonal .05 46 Goldbach's other conjecture .05 47 Distinct primes factors .05 48 Self powers .05 49 Prime permutations .05 50 Consecutive prime sum .05 51 Prime digit replacements .15 52 Permuted multiples .05 53 Combinatoric selections .05 54 Poker hands .10 55 Lychrel numbers .05 56 Powerful digit sum .05 57 Square root convergents .05 58 Spiral primes .05 59 XOR decryption .05 60 Prime pair sets .20 61 Cyclical figurate numbers .20 62 Cubic permutations .15 63 Powerful digit counts .05 64 Odd period square roots .20 65 Convergents of e .15 66 Diophantine equation .25 67 Maximum path sum II .05 68 Magic 5-gon ring .25 69 Totient maximum .10 70 Totient permutation .20 71 Ordered fractions .10 72 Counting fractions .20 73 Counting fractions in a range .15 74 Digit factorial chains .15 75 Singular integer right triangles .25 76 Counting summations .10 77 Prime summations .25 78 Coin partitions .30 79 Passcode derivation .05 80 Square root digital expansion .20 81 Path sum: two ways .10 82 Path sum: three ways .20 83 Path sum: four ways .25 84 Monopoly odds .35 85 Counting rectangles .15 86 Cuboid route .35 87 Prime power triples .20 88 Product-sum numbers .40 89 Roman numerals .20 90 Cube digit pairs .40 91 Right triangles with integer coordinates .25 92 Square digit chains .05 93 Arithmetic expressions .35 94 Almost equilateral triangles .35 95 Amicable chains .30 96 Su Doku .25 97 Large non-Mersenne prime .05 98 Anagramic squares .35 99 Largest exponential .10 100 Arranged probability .30