... function¹

A function $f(n)$ is said to be odd if $f(-n) = -f(n)$.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... even²

A function $f(n)$ is said to be even if $f(-n) = f(n)$

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.