The Atoms of Numbers

A prime number has exactly two factors: 1 and itself. The first primes are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29. Every other whole number greater than 1 is composite — it can be split into a product of primes.

Primes are the atoms of multiplication. Just as every molecule breaks down into elements, every number breaks down into primes. Take 60 = 2 × 2 × 3 × 5 — no other prime product gives 60. Around 300 BC, Euclid proved that primes never run out: no matter how large a prime you find, a larger one always exists.