Power Series Expansion for Error Function

Theorem

 * $\ds \map \erf x = \frac 2 {\sqrt \pi} \sum_{n \mathop = 0}^\infty \paren {-1}^n \frac {x^{2 n + 1} } {n! \paren {2 n + 1} }$

where:
 * $\erf$ denotes the error function
 * $x$ is a real number.