Primality & factorization

Prime Number Checker

Enter any whole number to instantly check if it's prime, list its factors, and see its full prime factorization.

Prime factorization–
All factors–
Previous prime–
Next prime–

How it works

1

Enter a whole number

Type any positive integer — small or large.

2

Trial division runs instantly

The checker tests divisibility up to the square root of your number to prove primality.

3

See the full breakdown

Get the prime factorization, every factor, and the nearest primes on either side.

FAQ

What is a prime number?

A prime number is a whole number greater than 1 that has exactly two factors: 1 and itself. Numbers with more than two factors are called composite.

Is 1 a prime number?

No. By definition, 1 has only one factor (itself), so it is classified as neither prime nor composite.

How does the tool check very large numbers?

It tests divisibility by every integer up to the square root of the number, which is enough to prove primality. Extremely large numbers (beyond about 15 digits) may take a moment or lose precision in standard JavaScript numbers.

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