# Project Euler Problem 14 (Collatz Problem)

The following iterative sequence is defined for the set of positive integers:

# Project Euler Problem 11 (Greatest product of four adjacent numbers in any direction in a 20 by 20 grid)

In the 20×20 grid below, four numbers along a diagonal line have been marked in red.

# Project Euler Problem 5 (LCM of numbers from 1 to 20)

2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.

# Project Euler Problem 12 (Triangle number to have over 500 divisors)

The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:

# Project Euler Problem 3

The prime factors of 13195 are 5, 7, 13 and 29.

# Project Euler Problem 7

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

# Project Euler Problem 9 (Pythagorean Triplet)

A Pythagorean triplet is a set of three natural numbers, a < b < c, for which,

# Project Euler Problem 18

By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum total from top to bottom is 23.