Prime numbers can only be divided by themselves and 1. Find out how to work out if a number is a prime in this Bitesize Primary Second Level Maths guide.

A basic feature of number theory, prime numbers are also a fundamental building block of computer science, from hashtables to cryptography.

The online computer game “Is this prime?” tests a player’s knowledge of prime numbers—and just surpassed 2,999,999 attempts. Give it a whirl.

Today, people use complex computing networks to search for prime numbers with millions of digits. But early mathematicians were running these calculations by hand.