# Definition:Even Integer/Definition 3

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## Definition

An integer $n \in \Z$ is **even** if and only if:

- $x \equiv 0 \pmod 2$

where the notation denotes congruence modulo $2$.

## Also see

## Historical Note

The concept of classifying numbers as **odd** or **even** appears to have originated with the Pythagoreans.

It was their belief that **even numbers** are **female**, and **odd numbers** are **male**.

A commentator on Plato used the term **isosceles number** for an **even number**, in correspondence with the concept of an isosceles triangle. In a similar way an odd number was described as **scalene**.

## Sources

- 1977: Gary Chartrand:
*Introductory Graph Theory*... (previous) ... (next): Appendix $\text{A}.5$: Theorems and Proofs: Example $\text A.3$ - 1996: John F. Humphreys:
*A Course in Group Theory*... (previous) ... (next): Chapter $2$: Maps and relations on sets: Example $2.23$