Showing what's behind the curtain

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

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

Calculate the sum of all the primes below two million.

Find the first four consecutive integers to have four distinct primes factors.

Find the sum of both diagonals in a square spiral.

Find the value of d < 1000 for which 1/d contains the longest recurring cycle.

Find the sum of all pandigital numbers with an unusual sub-string divisibility property.

Count how many ‘triangle words’ a list of common English words contain.

Find the sum of all eleven primes that are truncatable from both left to right and right to left.

Discover all the fractions with an unorthodox cancelling method.