Project Euler

Grid 0: Problems 1-99

Problem 1- Multiples of 3 and 5 - printing out all multiples of 3 and 5.
Problem 2 - Even Fibonacci - summing the Fibonacci numbers that are even and less than 4 million
Problem 3 - Largest Prime Factor - Largest prime factor of a given 12-digit number
Problem 4 - Largest Palindrome Product - Largest palindrome product (extracting substrings and sorting)
Problem 5 - LCM - Least common multiple of all the integers from 1 to 20
Problem 6 - SoS - Sum of squares and squares of sums
Problem 7 - Ten Thousand Primes - Find the 10,001st prime.
Problem 8 - Adjacent Digits - Largest product formed by 13 adjacent digits.
Problem 9 - Pythagorean Triplet Sum - Finding a Pythagorean triplet with a specified sum.
Problem 10 Sum of Primes - Sum of all primes below 2 million.

Problem 11 - Greatest Product in Grid - Finding the greatest product of 4 numbers on a grid.
Problem 12 - Highly Factorable Triangular Numbers - Finding highly factorable triangular numbers
Problem 13 - Sum of Big Numbers - Work out the first 10 digits of a sum of 100 50-digit numbers
Problem 14 - Longest Collatz Sequence - Finding the longest Collatz sequence for starting integers under 1 million
Problem 15 - Lattice Paths - Finding the number of variations on a route through a lattice.
Problem 16 - Summing the Digits - summing up the digits of a large power of 2, 2**1000
Problem 17 - Number Spelling - spelling out all the numbers from one to a thousand
Problem 18 - Shortest Path through a Triangle - find the path through a triangle of numbers that leads to the smallest sum
Problem 19 - Counting Sundays
Problem 20 - Sum of digits of 100! - straightforward use of BigInteger.

Problem 51- Prime Replacement - Finding the number of primes that can be formed by replacing particular digits of a number
Problem 52- Permuted Multiples - Find a number whose multiples 2x, 3x, 4x, 5x ad 6x are permutations of one another.
Problem 53 - Number of Combinations Over 1M - Find how many different n choose r values are greater than 1 million for n between 1 and 100.
Problem 54 - Comparing poker hands to determine a winner
Problem 55
Problem 56
Problem 57
Problem 58 - Counting how many composite numbers have exactly 8 factors
Problem 59 - Decrypting 3-letter secret key (Vigenere cipher)
Problem 60 - Prime pair sets - finding five primes such that any prime pair can be concatenated to form a new prime

Problem 61 - Six cyclic 4-digit numbers, each of which are polygonal numbers (triangle, square, pentagonal, hexagonal, heptagonal, octagonal)
Problem 62 - Cyclic permutations of cubes - find cubes that permute to other cubes.
Problem 63 - Powerful digit counts - finding n-digit numbers that are n-th powers
Problem 64 - Continued Fractions - Odd period square roots - finding the continued fraction representation of an odd number, and determining if it has an odd period. First 1,000 numbers, so these sequences get LONG.
Problem 65 - Convergents of e - computing the 100th convergent (rational representation of continued fraction) for e and the square root of 2.
Problem 66 - Diophantine equation - a nice problem involving quadratic Diphantine equations called Pell equations. These equations can be solved using the technique of continued fraction representations. It is much easier to solve this problem, then 64 and 65, rather than the other way around.
Problem 67 - Maximum path sum - a retake on Project Euler/18 with a larger triangle for which a brute force solution technique is impossible.
Problem 68
Problem 69
Problem 70

Problem 100 - Combinations of Red and Blue Discs - find arrangements of blue and red discs that lead to a probability of exactly 50% that a blue disc is removed, two times in a row.
Problem 101 - Bad Optimal Polynomials - Lagrangian polynomial interpolation for a sequence of numbers, interpolation of an optimal N-1 polynomial given N points of data.
Problem 102 - Triangles Containing Origin - given 3 endpoints, determine if a triangle contains the origin.
Problem 103
Problem 104
Problem 105
Problem 106
Problem 107
Problem 108
Problem 109

Problem 170
Problem 171
Problem 172 - Few Repeated Digits - how many 18 digit numbers have no digit occurring more than 3 times in n?
Problem 173
Problem 174
Problem 175
Problem 176
Problem 177
Problem 178
Problem 179

Problem 254 - Maximum Source of Sums of Digits of Sums of Digits of Sums of Factorial Digit Sums

Problem 500 - Smallest Number with 2n Factors - Finding the smallest number with 2^n divisors
Problem 501 - Eight Divisors - Finding numbers with exactly 8 divisors, less than 1 trillion
Problem 502 - Castles - finding the maximum number of castles that can be formed on extremely large grids