Prime Number Checker

About this calculator

This tool checks whether a number is prime — meaning it has no positive divisors other than 1 and itself — by testing it against candidate divisors, and if the number is not prime, it also breaks the number down into its prime factorization, the unique set of prime numbers that multiply together to produce it. Every whole number greater than 1 is either prime or can be expressed as exactly one such product, a fact known as the fundamental theorem of arithmetic.

It is used by students learning number theory and working through factoring problems, and by programmers and hobbyists exploring topics like cryptography, where the difficulty of factoring very large numbers into their prime components underpins the security of algorithms like RSA. It also comes up in simpler practical contexts, like reducing a fraction to lowest terms or finding the least common multiple of two numbers, both of which rely on knowing prime factorizations.