Question
What is a prime number?
A prime number is a whole number greater than 1 that has exactly two positive factors: 1 and itself.
Math
Use OmniCalc's prime number calculator to check whether a whole number is prime and see the factors behind the result.
Prime number calculator
Enter a whole number to see whether it is prime, how many factors it has, and which factors explain the result.
Why this result matters
A fast prime-check tool that supports factor and number-theory workflows. Use the tool above to enter a few clear inputs and get a practical answer you can use right away.
This prime number calculator helps students and everyday users test a number quickly without manually checking divisors one by one. It is useful for factor work, divisibility checks, number-pattern learning, and quick prime/composite decisions.
Formula and method
The calculator rounds the input to a whole number, checks possible divisors up to the square root, and uses the resulting factor list to decide whether the number has exactly two positive factors.
Example
If you enter 29, the calculator shows that it is prime because its only positive factors are 1 and 29.
FAQ
Short answers to the questions people often ask before or after using the tool.
Question
A prime number is a whole number greater than 1 that has exactly two positive factors: 1 and itself.
Question
A composite number has more than two positive factors, which means it can be divided evenly by something other than 1 and itself.
Question
Prime numbers help with factorization, divisibility, cryptography, and many basic number-theory ideas in math.
Related calculators
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Use OmniCalc's prime factorization calculator to break a whole number into the prime values that multiply back to it.
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Use OmniCalc's factor calculator to list every whole-number factor of a number and see the factor pairs that build it.
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Use OmniCalc's divisibility calculator to see which common divisors a whole number passes without working through long division by hand.
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Use OmniCalc's common factor calculator to list every whole-number factor shared by the numbers in your set.