Enter any positive integer below to instantly check if it's a prime number. The calculator shows all factors and highlights which ones are prime.
Prime Number Calculator
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What is a prime number?
A prime number is a positive integer greater than 1 that has exactly two factors: 1 and itself. The first few primes are 2, 3, 5, 7, 11, 13, 17, 19, and 23.
The number 1 is special - it's neither prime nor composite by mathematical convention. This definition keeps the fundamental theorem of arithmetic clean: every integer greater than 1 has a unique prime factorization.
Using the calculator
Enter any positive integer in the Number field. The calculator instantly shows:
- Whether the number is prime or composite
- All factors of the number
- Prime factors highlighted in green
