Below is a list of all Project Euler problems I’ve solved successfully. The problems are devised as to make simple loops testing all numbers impractical, thus forcing you to use custom algorithms. The key insight seems to usually lie in some number-theoretic property of the problem at hand.

  1. Multiples of 3 and 5
  2. Even Fibonacci Numbers
  3. Largest Prime Factor
  4. Largest Palindrome Product
  5. Smallest Multiple
  6. Sum of Squares Difference
  7. The 10,001st Prime
  8. Largest Product in a Series
  9. Special Pythagorean Triplet
  10. Summation of Primes
  11. Largest Product in a Grid
  12. Longest Collatz Sequence