Prime Number Tools
NewCheck if a number is prime, find primes up to N, prime factorization, and nearest prime finder.
Prime number utilities
Prime Number Tools
Check if a number is prime, find primes up to N, prime factorization, and nearest prime finder.
Prime check
Check whether a number is prime.
Prime factorization
Factorize any positive integer.
Neighboring primes
Find the previous and next prime around a number.
Prime list
0Frequently Asked Questions
How high can I generate a prime list here?
Up to 10,000. The UI shows that limit, and the generator enforces it with a hard error if you go higher.
Why won't it factorize 1, 0, negative numbers, or decimals?
Because the factorization path requires an integer greater than 1. The input parser also rejects non-integers everywhere with 'Enter a whole number.'
If I enter a prime number, will 'Next / Previous' include that same prime?
No. The neighbor search starts at n-1 and n+1, so it returns the surrounding distinct primes. For 13, you'll get 11 and 17, not 13 itself.
What does it say for numbers below 2?
Prime checks mark them as not prime, and the previous-prime search reports none below 2. The next-prime search still climbs upward and returns the next valid prime.
How is it calculating these results?
Prime checks and factorization use straightforward divisibility testing up to the square root, while the list generator uses a sieve. That's why single checks are flexible, but bulk generation is capped at 10,000 for the browser UI.
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