Prime Number Checker – Is It Prime?
Enter any positive integer to instantly check if it is a prime number. See prime factorization for composite numbers and navigate to nearby primes.
17
is a PRIME number
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How to Use
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Enter any positive integer in the input field
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See instantly whether the number is prime or composite
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For composite numbers, see the prime factorization. Click nearby primes to check them too
Frequently Asked Questions
What is a prime number?
A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. Examples: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29.
Is 1 a prime number?
No. By definition, prime numbers must be greater than 1. The number 1 is called a "unit" and is neither prime nor composite.
What is prime factorization?
Prime factorization is the process of expressing a composite number as a product of prime numbers. For example, 12 = 2 × 2 × 3. Every composite number has a unique prime factorization (Fundamental Theorem of Arithmetic).
How is it determined if a number is prime?
This tool uses trial division: it tests all divisors from 2 up to the square root of the number. If none divide evenly, the number is prime. This is efficient for numbers up to hundreds of millions.
Check if a number is prime
A prime number checker tells you instantly whether a number is prime — divisible only by 1 and itself — and, if not, often shows its factors. Enter any whole number and get an immediate, reliable answer.
It saves the slow work of testing divisors by hand, even for large numbers.
Why check for primes
- Maths homework and number theory.
- Cryptography learning and curiosity.
- Checking factors of a number quickly.
- For wider maths use the scientific calculator; to change base, the number base converter.
The check runs in the browser
The check runs in your browser, so the answer is immediate and private.