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Prime Number Checker
Check whether any number is prime, view its prime factorisation, and find the nearest prime numbers above and below it.
Frequently Asked Questions
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, and 29. 2 is the only even prime number.
This tool uses trial division and can check numbers up to 10 million quickly. For very large numbers (millions of digits), specialist primality tests like Miller-Rabin are needed.
Prime factorisation (also called integer factorisation) is the decomposition of a number into a product of prime numbers. For example, 360 = 2³ × 3² × 5. Every integer greater than 1 has a unique prime factorisation.