Prime Number Checker
Enter a positive whole number to instantly check whether it is prime or composite.
How to Use the Prime Number Checker
Enter a non-negative whole number. The tool tests divisibility up to the square root of the number and reports whether it is prime or composite.
Practical Example
97 is prime because no integer greater than 1 and less than or equal to √97 divides it evenly. By contrast, 91 is composite because 91 = 7 × 13.
Factors That Affect the Result
The input must be a whole number within the browser's safe integer range. Values below 2 are neither prime nor composite.
Related Tools
Prime Factorization Calculator · GCF Calculator · LCM Calculator · Square Root Calculator · Exponent Calculator
Frequently Asked Questions
Is 1 prime?
No. One is neither prime nor composite.
Is 2 prime?
Yes. Two is the smallest and only even prime number.
Are negative numbers prime?
Under the standard elementary definition, prime numbers are positive integers greater than 1.
How Prime Number Checking Works
A prime number is an integer greater than 1 with exactly two positive divisors: 1 and itself. Numbers such as 2, 3, 5 and 7 are prime, while 9 is composite because it is divisible by 3. To test whether a number is prime, it is not necessary to try every smaller integer. If a number has a factor other than 1 and itself, at least one factor will be less than or equal to its square root. Efficient checks therefore test possible divisors only up to √n. The number 2 is the only even prime number, while 0, 1 and negative integers are not prime under the standard definition. Prime checking is useful in number theory, factorization and many computing applications, although very large integers may require specialized algorithms beyond simple trial division.