**Prime numbers**History / Mystery / Mathematics / Cryptography

## Definition

An integer number is a *multiple of 5* if it is **divisible by 5**.

### A mathematical trick to determine whether a number is divisible by 5

In order to easily find out whether a number is a multiple of 5, we just need to look at its last digit. If it is equal to 0 or 5, then the number is a multiple of 5. Otherwise, it is not a multiple of 5

For example, 2 025 is a multiple of 5 because its last digit is 5. Conversely, 2 026 is not a multiple of 5 because its last digit is 6, and therefore neither equal to 5 nor to 0.

### A few suggestions

- Is 0 a prime number?
- Is 1 a prime number?
- Is 2 a prime number?
- Is 72 a prime number?
- Is 4994 a prime number?
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- Is 661971430 a prime number?