Numbers › Number theory

Number theory

The study of whole numbers — primes, divisibility, modular arithmetic — and the surprising laws hiding inside them.

Where to dig in

Primes

The atoms of arithmetic.

Factors

Every divisor of a number.

Divisibility rules

Quick checks without dividing.

Modulo

Clock arithmetic — what's the remainder?

Fibonacci

Each one is the sum of the last two.

Factorial

n! grows faster than anything.

What number theorists love

They love finding patterns in whole numbers that hold forever — not just for the first thousand, but for every number that ever could be. A lot of those patterns turn out to be hard to prove, even when they're easy to check.