Mathematics
What is A prime number?
A prime number is a whole number greater than 1 that can only be divided evenly by 1 and itself. Primes like 2, 3, 5, and 7 are the 'building blocks' of all numbers — and they quietly secure modern online encryption.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains a prime number.
Key things to understand
- 1It has exactly two divisors: 1 and itself.
- 22, 3, 5, 7, 11, 13… are the first primes (2 is the only even one).
- 3Every whole number is a unique product of primes.
- 4There are infinitely many primes, proven over 2,000 years ago.
- 5Huge primes underpin internet encryption.
Frequently asked questions
- Why is 1 not a prime number?
- A prime must have exactly two distinct divisors; 1 has only one (itself), so by definition it's excluded.
- How are primes used in encryption?
- Multiplying two huge primes is easy, but factoring the result back is extremely hard — that gap secures much of online communication.
- Are there infinitely many primes?
- Yes. Euclid proved over two thousand years ago that the primes never run out.