What is a prime number?

A prime has exactly two distinct divisors: 1 and itself. Examples: 2, 3, 5, 7, 11, 13.

What is the Sieve of Eratosthenes?

An ancient algorithm that finds all primes up to N by iteratively marking multiples of each prime as composite.

What numbers are supported?

The primality check works up to Number.MAX_SAFE_INTEGER. The sieve is practical up to about 10,000,000 in the browser.

Prime Checker

Check if a number is prime and generate primes up to N.

primality checker

sieve of eratosthenes

Related Tools

phiFibonacci Generator

Generate Fibonacci sequences and check if a number is Fibonacci.

+-Average Calculator

Calculate mean, median, mode, range, and standard deviation.

FAQ

What is a prime number?: A prime has exactly two distinct divisors: 1 and itself. Examples: 2, 3, 5, 7, 11, 13.
What is the Sieve of Eratosthenes?: An ancient algorithm that finds all primes up to N by iteratively marking multiples of each prime as composite.
What numbers are supported?: The primality check works up to Number.MAX_SAFE_INTEGER. The sieve is practical up to about 10,000,000 in the browser.

Enter any positive integer to instantly determine if it is prime. If it is not prime, the tool shows its full prime factorization. A second panel uses the Sieve of Eratosthenes to list all primes up to a given limit, with a count of primes found. Useful for number theory, coding challenges, and math exploration.