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Prime Number Checker

Test whether a number is prime.

Check whether any positive integer up to a trillion is prime, and if not, the smallest factor that proves it composite.

Daniel Oh By Daniel Oh
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Trial division by primes up to √n: a number is composite if any of those divides it evenly.

In depth

Check whether any positive integer up to a trillion is prime, and if not, the smallest factor that proves it composite.