Check if any number is prime. This free prime number checker tells you instantly whether a number is prime, and if not, lists its divisors and prime factorization.
Check a number
Enter a positive whole number. The checker tells you whether it’s prime, and if not, lists its factors and prime factorization.
Result
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Enter a number
Prime factorization
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Number of divisors
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Smallest factor > 1
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All divisors
A prime number has exactly two divisors: 1 and itself. 1 is not prime (only one divisor), and the smallest prime is 2 — the only even prime.
Use this free prime number checker to find out if a number is prime. Enter any whole number and it tells you instantly, and if it’s not prime, shows its factors and prime factorization.
What this prime number checker does
A prime number checker tests whether a number is prime — divisible only by 1 and itself. If the number is composite, it lists all its divisors and gives the prime factorization.
What is a prime number?
Prime = exactly two divisors (1 and itself)
Composite = more than two divisors
1 is neither prime nor composite
97 is prime — nothing divides it evenly except 1 and 97. 100 is composite: 2² × 5².
Primes and factorization
Number
Prime?
Prime factorization
17
Yes
17
51
No
3 × 17
100
No
2² × 5²
360
No
2³ × 3² × 5
Quick facts about primes
2 is the only even prime; every other prime is odd. The number 1 is not prime because it has only one divisor. Primes are the building blocks of all whole numbers — every integer above 1 is a product of primes.
How to use the prime number checker
Enter a positive whole number.
See instantly whether it’s prime.
If composite, review its factors and prime factorization.
Prime Number FAQ
How do I know if a number is prime?
A number is prime if it has exactly two divisors — 1 and itself. Enter it here and the checker tests divisibility instantly. For example, 97 is prime.
Is 1 a prime number?
No. 1 has only one divisor (itself), so it doesn't meet the definition of a prime, which requires exactly two distinct divisors.
What is the smallest prime number?
2 — and it's the only even prime. Every other even number is divisible by 2, so all other primes are odd.
What is prime factorization?
Writing a number as a product of primes. For 100 it's 2² × 5²; for 360 it's 2³ × 3² × 5. The checker shows this for composite numbers.
What's the difference between prime and composite?
A prime has exactly two divisors; a composite number has more than two. Every whole number above 1 is one or the other.
Is the prime number checker free?
Yes, this prime number checker is completely free, needs no sign-up, and gives instant results in your browser.
