Mittag-Leffler Expansion for Secant Function

Theorem

 * $\displaystyle \pi \sec \paren {\pi z} = 4 \sum_{n \mathop = 0}^\infty \paren {-1}^n \frac {2 n + 1} {\paren {2 n + 1}^2 - 4 z^2}$

where:
 * $z \in \C$ is not a half-integer
 * $\sec$ is the secant function.