What is a Prime Number?
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. The first few primes are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29…
2 is the only even prime number. All other even numbers are divisible by 2 and therefore composite.
How This Checker Works
This tool uses trial division: it tests whether the number is divisible by any integer from 2 up to its square root. If no such divisor is found, the number is prime. The square root optimisation is valid because if n = a × b and a ≤ b, then a ≤ √n.