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.

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:

2 | if the number is even |

3 | if the sum of the digits is divisible by 3 |

4 | if the last two digits are a number divisible by 4 |

5 | if the last digit is 5 or 0 |

6 | if the number is even and divisible by 3 |

8 | if the number is divisible by 4 and the result is even |

9 | if the sum of the digits is divisible by 9 |

10 | if the last digit is 0 |

### Credits

- Modified by Michael McKelvey (4/24/2006)