Prime Number Checker

Check whether a number is prime, see its prime factorisation and find the nearest primes.

What is the Prime Number Checker?

A prime number has exactly two divisors: 1 and itself. 2 is the only even prime.

How does it work?

The checker uses a deterministic Miller–Rabin test that is proven correct for numbers up to 24 digits. Composite numbers are factorised by trial division.

Formula

n is prime ⇔ n > 1 and its only divisors are 1 and n

Example

97 is prime. 360 = 2³ × 3² × 5, which has 24 divisors.

Frequently asked questions

Is 1 a prime number?

No. By definition a prime must have exactly two distinct divisors, and 1 has only one.

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