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Prime Number List & Checker

List every prime number in a range (Sieve of Eratosthenes), or check whether a single number is prime — instant results.

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Primes, Listed or Checked

Switch between two modes: list every prime in a range using the Sieve of Eratosthenes (fast and exact up to very large ranges), or check a single number by trial division up to its square root.

Frequently Asked Questions

What counts as a prime number?

A natural number greater than 1 with exactly two divisors: 1 and itself. 1 is not prime, and neither is any negative number.

How large a range can I list?

Up to 1,000,000 — the sieve stays fast and your browser stays responsive within that range.

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