Prime Number Checker

Check if a number is prime and list factors if not.

Overview

Determines whether an integer is prime or composite, testing trial divisibility up to sqrt(n) with 6k ± 1 primality optimizations and prime factorizations.

Formula & Calculation Method

Primality Test: Check divisibility by 2, 3, and all integers 6k ± 1 <= sqrt(n)

A prime number is an integer strictly greater than 1 that has no positive divisors other than 1 and itself.

Worked Example: Testing Primality of 97

Inputs: Integer n = 97

  • Calculate square root: sqrt(97) ≈ 9.84 (test primes <= 9)
  • Test prime divisors: 2 (no), 3 (no), 5 (no), 7 (97 / 7 = 13.85, no)
  • No divisors found below sqrt(97).
  • Result: 97 is a Prime Number.

Summary: Number = 97 | Status = PRIME | Factors = 1 and 97 only

Common Use Cases

  • Cryptography & Security: Understand the prime factorization foundations of RSA public-key encryption.
  • Number Theory Homework: Verify prime classifications and find next adjacent prime numbers.
  • Algorithm Benchmarking: Demonstrate computational complexity and trial division optimizations.

Frequently Asked Questions

Why is 1 not considered a prime number?

Because if 1 were prime, the Fundamental Theorem of Arithmetic (unique prime factorization) would break, as you could multiply by 1 infinitely.

Why is testing up to sqrt(n) sufficient to prove primality?

Because if n had a factor larger than sqrt(n), its corresponding factor pair would have to be smaller than sqrt(n), which would have already been detected.

What are Twin Primes?

Pairs of prime numbers that differ by exactly 2 (such as 3 and 5, 11 and 13, 17 and 19, or 41 and 43).

Related Calculators & Tools