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

## Definition

An integer number is an *even number* whenever it is **divisible by 2**.

Otherwise, it is said to be an *odd* number.

For example, 2 020 is even because it is divisible by 2 since 2 020 = 1 010 × 2 + 0, therefore the remainder is zero (0). Conversely, 2 021 is not divisible by 2 because 2 021 = 1 010 × 2 + 1, hence the remainder is 1, therefore non-zero; as a consequence, 2 021 is an odd number.

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