# Euclid’s Proof of Infinitely Many Primes

## How we know there are infinitely many prime numbers, explained briefly

Last week I wrote about sexy primes, a type of prime number. I mentioned that we’ve known that there are infinitely many prime numbers since about 300 B.C., thanks to a proof documented by Euclid. It’s a nice proof! It’s also a great example of a *proof by contradiction*. So I’m…