AtlasCalc🧮 MathbeginnerOffline
Prime Numbers
Check if a number is prime, or list all primes up to N.
Inputs
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Result
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Enter values and press Calculate — the result appears here.
How it works
The formula behind this calculator.
Trial division up to √n; or Sieve of Eratosthenes for ranges
- n
- The integer to test
A prime has exactly two divisors: 1 and itself. To test primality, try dividing by every integer from 2 up to √n. None divide evenly → prime.
Example: 17 is prime: no d from 2 to √17 ≈ 4.12 divides it
Ref: Fundamental Theorem of Arithmetic
Tips
- 💡 1 is not a prime number. 2 is the only even prime.
- 💡 Numbers ending in 0, 2, 4, 6, or 8 (except 2 itself) are never prime.
FAQ
What is the largest known prime?
As of 2024, the largest known prime has over 24 million digits. It's a Mersenne prime: 2⁸²⁵⁸⁹⁹³³ − 1.