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

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

Prime numbers are fundamental to the most common type of encryption used today: the RSA algorithm. The RSA algorithm was named after the three mathematicians who first publicly unveiled it in 1977.

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.

Prime numbers are a central topic of study in math. Despite being an object of fascination for millennia, there are still a lot of unsolved problems involving primes. Prime numbers are one of the ...