Prime Number Checker

Check if any number is prime, view its prime factorization, find nearby primes, and list all primes in a range. Supports numbers up to 1 quadrillion.

Check if a number is prime, see its factorization, find nearby primes, or list all primes in a range.

Quick Test
Uses trial division for primality testing. Supports numbers up to 10^15. All calculations run locally in your browser.

How to Use This Tool

  1. 1

    Enter a number

    Type any positive integer up to 1 quadrillion (10^15) into the input field.

  2. 2

    Check primality

    Click 'Check' or press Enter to instantly see whether the number is prime or composite.

  3. 3

    View factorization

    If the number is not prime, the tool shows its complete prime factorization and nearby prime numbers.

  4. 4

    Find primes in a range

    Switch to Range Mode to list all prime numbers between any two values (up to 100,000 span).

Frequently Asked Questions

What is a prime number?
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. Examples: 2, 3, 5, 7, 11, 13.
What is the largest number I can check?
This tool supports numbers up to 1 quadrillion (1,000,000,000,000,000 or 10^15). Results are instant for most numbers.
What is prime factorization?
Prime factorization breaks a composite number into a product of prime numbers. For example, 12 = 2 × 2 × 3. Every integer greater than 1 has a unique prime factorization.
Is 1 a prime number?
No. By mathematical convention, 1 is neither prime nor composite. The smallest prime number is 2, which is also the only even prime number.