Prime Number Checker & Generator
Check if a number is prime and see its factors, or generate a list of primes up to a limit.
Check a Number
Generate a List of Primes
How to Use the Prime Number Tool
- Enter a number to check whether it's prime, with its factors if not.
- Enter a limit to generate every prime number up to that value.
Frequently Asked Questions
How does the checker actually verify primality?
It uses trial division, testing whether any whole number from 2 up to the square root of your number divides it evenly — if none do, the number is prime. This is a genuinely correct method, not an approximation, though it becomes slower for extremely large numbers.
Are 0 and 1 prime numbers?
No — by definition, a prime number must be greater than 1. Neither 0 nor 1 counts as prime or composite; 1 is a special case sometimes called a "unit."
How high can the prime list generator go?
It's capped at 1,000,000 to keep the calculation fast and avoid generating an unreasonably long list for your browser to render.
Is my data sent anywhere?
No — all calculations happen entirely in your browser using JavaScript, so nothing you enter is ever sent to a server.