# series

A series is the sum of all or some of the terms of a sequence.
Thus, the series 1 + 4 + 9 + 16 + ... is formed from the sequence 1, 4,
9, 16 ,... A series may or may not converge to a particular value as more
and more terms are included. A series is said to be **absolutely convergent** if the sum of the absolute values of the terms converges; in this case the
series converges no matter how the terms of the sum are arranged. Series
that are **conditionally convergent** only converge for some
arrangements of the terms and, even then, converge to different values for
different arrangements.

A series formed from increasing powers of a variable is a power series; such power series are used to represent many functions.