University of Illinois at Urbana-Champaign
Office for Mathematics, Science, and Technology Education
College of Education @ University of Illinois

Prime Number Determiner

This page presents the user with the chance to determine if a certain number is prime. The calculation is accurate for numbers 16 digits or shorter.

Please enter a number and then press the Determine button:

Enter number here:

Check ALL Factors:  
Check This Many Factors:
Reset the Form:  

Result is:

Elapsed Time:

Algorithm Output:

As you read the result, remember the typical divisibility tests for numbers to diagnose if they are prime or not.

A natural number is divisible by:

2if the number is even
3if the sum of the digits is divisible by 3
4if the last two digits are a number divisible by 4
5if the last digit is 5 or 0
6if the number is even and divisible by 3
8if the number is divisible by 4 and the result is even
9if the sum of the digits is divisible by 9
10if the last digit is 0



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