Calculate the sum of all the primes below two million.
What is the greatest product of four numbers on the same straight line in the 20 by 20 grid?
What is the value of the first triangle number to have over five hundred divisors?
Find the first ten digits of the sum of one-hundred 50-digit numbers.
Longest Collatz sequence
Starting in the top left corner in a 20 by 20 grid, how many routes are there to the bottom right corner?
What is the sum of the digits of the number 2^1000?
How many letters would be needed to write all the numbers in words from 1 to 1000?
Find the maximum sum travelling from the top of the triangle to the base.
How many Sundays fell on the first of the month during the twentieth century?