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Prime Number Checker
Test if a number is prime – instantly.
Check a Number
Enter a whole number
17 is a prime number.
17 is a prime number.
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How it works
Enter a whole number
(greater than 1).
Instant check
– the tool tests divisibility up to the square root of the number.
If prime
– the result turns green and says it's prime.
If composite
– the result turns red and shows the smallest divisor (other than 1).
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– keep a record of the result.