Runs locally
Prime Number Checker
Deterministic test up to 64-bit integers.
Ctrl+Enter runs. Ctrl+Shift+Backspace clears.
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Uses a deterministic Miller–Rabin test for integers up to 2^64. Larger values are refused instead of guessed.
About this tool
Enter any integer and learn whether it is prime. The check uses a deterministic Miller–Rabin test, so the answer is exact for every number up to 2^64.
How to use it
- 01
Type the integer you want to check.
- 02
The answer appears as you type.
- 03
For a composite number, open Prime Factors to see its divisors.
FAQ
Frequently asked questions
Is the answer guaranteed?
Yes. For integers up to 2^64 the deterministic Miller–Rabin test gives an exact answer, not a probability.
What about larger numbers?
Values above 2^64 are refused instead of guessed, so you never get an unreliable result.