Showing what's behind the curtain

Calculate the sum of all the primes below two million.

Find the greatest product of four adjacent numbers in the same direction in a grid.

Find 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.

Find the starting number, under one million, that produces the longest Collatz sequence.

Find the number of routes from the top left corner to the bottom right corner in a rectangular grid.

Sum of the digits in 2^1000.

Count how many letters would be needed to write all the numbers in words from 1 to 1000.

Maximum sum from top to bottom of triangular array.

Find how many Sundays fell on the first of the month during the twentieth century.