sequence

A sequence is a collection of objects that have a specified order. Like a set, it contains members called elements, but unlike a set, repetition is allowed and order does matter.

Formally,
a sequence $(S_n)$ is a function $S:x\mapsto S_x$, where the index $x$ is from an interval of integers such that the ordering of $S_a\sim S_b$ is the same as $a\sim b$.

The number of elements in a sequence is its length.
The position of an element in a sequence is the element's index or rank.
The $n^{th}$ element of a sequence $S$ is denoted $S_n$.

See also:

• series