Prime Number Checker
Check whether a number is prime and find its factors.
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How it works
Enter a whole number and the tool tests whether it is prime by trial division up to its square root, which is enough to find any factor. If the number is not prime, it lists the factors and shows the prime factorization (the number written as a product of primes). It works efficiently for large numbers because checking only up to the square root keeps the work small. All computation runs locally in your browser.
prime if no divisor from 2 to √n
Common use cases
- Checking whether a number is prime for homework or a puzzle.
- Finding the prime factorization of a number.
- Listing all factors of a value.
Frequently asked questions
How large a number can it handle?
It comfortably handles numbers up to the safe-integer range using trial division to the square root, which keeps even large checks fast.
What is prime factorization?
It is the number written as a product of prime numbers — for example 60 = 2 × 2 × 3 × 5. Every whole number above 1 has a unique prime factorization.
Is 1 prime?
No. By definition a prime has exactly two distinct positive divisors, 1 and itself. The number 1 has only one divisor, so it is neither prime nor composite.