Calculators

Prime Number Checker

Test whether a number is prime.

Whole number

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Verdict

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Nearest lower prime

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Nearest higher prime

This free prime number checker tells you whether a whole number is prime — a number greater than 1 whose only divisors are 1 and itself. Enter a value and it uses trial division up to the square root to test primality quickly. If the number is not prime it shows the factor pairs and prime factorization, and either way it reports the nearest lower and higher primes.