Find Out Whether a Number Really Is Prime

With this calculator, you can enter a number and find out whether it is prime or not.

Definition of a prime number

A prime number is a number that is only divisible by itself and by 1. For example, 17 is a prime number because it can only be divided by 17 or by 1. On the other hand, 18 is not a prime number because it is divisible by 1, by 18, and also by 2 and 3.

How to test if a number is prime?

To test a number, type it in the field labeled "Number" (next to "To test"). The tool automatically analyzes the number you enter to determine whether it is prime or not. If the number is prime, a message appears on a green background; otherwise, it appears on a red background.

For example, you can check whether the number 7 is prime or not.

Why know about prime numbers?

They are useful for reducing a fraction to its lowest terms. A fully reduced fraction cannot be simplified any further.

CLEAR and SAVE buttons

To reset the tester, press the Clear button. If you want to keep a record of your checks, press Save. You can then export the generated table in CSV or PDF format.

List

Here is a non-exhaustive list of prime numbers from 2 up to 29.

• 2
• 3
• 5
• 7
• 11
• 13
• 17
• 19
• 23
• 29

Of course, the list is not complete and there are many more prime numbers after 29.

Shortcuts

m ⇝ Clear

f ⇝ Save