Prime Number Checker
Check if a number is prime or find primes in a range.
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Prime Numbers
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Frequently Asked Questions
What makes a number prime? +
A prime number is a whole number greater than 1 that has exactly two factors: 1 and itself. For example, 7 is prime because nothing divides it evenly except 1 and 7.
Is 1 a prime number? +
No. By definition, a prime number must have exactly two distinct factors. The number 1 only has one factor (itself), so it is not considered prime.
How large of a number can this check? +
This tool can reliably check numbers up to about 10 billion. It uses trial division up to the square root of the number, which is fast enough for numbers of that size.
What are the factors shown for non-prime numbers? +
For composite (non-prime) numbers, the tool shows all factor pairs. For example, 12 has factors: 1x12, 2x6, 3x4. This helps you see exactly why the number is not prime.
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