Power Series Expansion for Complementary Error Function

Theorem

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

where:
 * $\erfc$ is the complementary error function
 * $x$ is a real number.