Prime Number Checker
Enter a number to find out whether it's prime, and see its factors.
How to use Prime Number Checker
- Enter a number.
- See whether it's prime, and if not, its factors are listed.
Frequently asked questions
How does it check whether a number is prime?
By trial division — it tests divisibility by 2, then by every odd number up to the square root of the input, which is enough to rule out any factor pair.
Why don't I see a factors list when I check a prime number?
Factors are only shown for non-prime numbers — since a prime's only factors are 1 and itself, listing them wouldn't add anything.
How high can the "primes up to" list go?
It's capped at 1000, even if you type a larger number into that field.
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