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Prime Number Checker
Check if a number is prime and find all primes in a range.
⭐ Used by 4,890 people

The Prime Number Checker instantly checks if any number is prime and finds all prime numbers within a given range.

What is a Prime Number?

A prime number is a natural number greater than 1 that has no divisors other than 1 and itself.

Prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29...
Not prime (composite): 4, 6, 8, 9, 10, 12, 14, 15...
Special: 1 is neither prime nor composite

Quick Facts About Primes

  • 2 is the only even prime number
  • There are infinitely many prime numbers
  • Largest known prime has 24 million digits!
  • Prime numbers are used in encryption and cybersecurity

How to Check if a Number is Prime

Check if the number is divisible by any number from 2 to its square root. If no divisor found, it's prime!

📖 Complete Guide
Formulas, examples, tips & FAQs
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Frequently Asked Questions

What is a prime number?

A prime number is a whole number greater than 1 that has exactly two factors, 1 and itself, such as 2, 3, 5, 7, and 11.

How does the prime checker work?

It tests whether the number can be divided evenly by any number other than 1 and itself. If no such divisor exists, the number is prime.

Is 1 a prime number?

No. By definition a prime must have exactly two distinct factors, but 1 has only one factor, so it is not considered prime. The smallest prime number is 2.