Prime Number Checker
Type any whole number to find out whether it is prime. If it is not, you get the prime factorization in exponent form plus a list of every divisor.
How to check a prime number
- Enter a whole number that is 1 or greater.
- Read the PRIME or NOT PRIME result at the top.
- Review the prime factorization and the list of divisors below it.
Examples
A prime number
97
97 is PRIME. Its only divisors are 1 and 97.
A composite number
360
360 is NOT PRIME. Factorization: 2^3 x 3^2 x 5.
Frequently asked questions
What is a prime number?
A prime number is a whole number greater than 1 whose only positive divisors are 1 and itself. The first few primes are 2, 3, 5, 7, 11 and 13.
Why is 1 not a prime number?
A prime must have exactly two distinct divisors, 1 and itself. The number 1 has only one divisor, so it fails that rule and is classed as neither prime nor composite.
What is prime factorization used for?
Writing a number as a product of primes is the basis for finding greatest common divisors and least common multiples, simplifying fractions, and the cryptography that secures online traffic.
What is the largest known prime?
Record primes are enormous Mersenne primes with tens of millions of digits, found by distributed projects like GIMPS. This tool is built for everyday numbers, not record-sized ones.
Does the checker work offline and keep my numbers private?
Yes. The calculation runs entirely in your browser, so nothing you type is sent to a server.
How large a number can I check?
It is accurate for any integer JavaScript represents exactly, up to about nine quadrillion. The divisor list is most useful for smaller numbers.
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