Project-Euler-Solutions

Solving Project Euler problems in C#

Problems

• 1. Find the sum of all the multiples of 3 or 5 below 1000. (Problem, Solution)
• 2. By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms. (Problem, Solution)
• 3. What is the largest prime factor of the number 600851475143? (Problem, Solution)
• 4. Find the largest palindrome made from the product of two 3-digit numbers. (Problem, Solution)
• 5. What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20? (Problem, Solution)
• 6. Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum. (Problem, Solution)
• 7. What is the 10 001st prime number? (Problem, Solution)
• 8. Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product? (Problem, Solution)
• 9. Find the product abc. (Problem, Solution)
• 10. Find the sum of all the primes below two million. (Problem, Solution)
• 11. What is the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid? (Problem, Solution)
• 12. What is the value of the first triangle number to have over five hundred divisors? (Problem, Solution)
• 13. Work out the first ten digits of the sum of the following one-hundred 50-digit numbers. (Problem, Solution)
• 14. Which starting number, under one million, produces the longest chain? (Problem, Solution)
• 15. How many such routes are there through a 20×20 grid? (Problem, Solution)
• 16. What is the sum of the digits of the number 21000? (Problem, Solution)
• 17. If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used? (Problem, Solution)
• 18. Find the maximum total from top to bottom of the triangle (Problem, Solution)
• 19. How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)? (Problem, Solution)
• 20. Find the sum of the digits in the number 100! (Problem, Solution)