Power Series Expansion for Sine Integral Function

Theorem

 * $\displaystyle \map \Si x = \sum_{n \mathop = 0}^\infty \paren {-1}^n \frac {x^{2 n + 1} } {\paren {2 n + 1} \times \paren {2 n + 1}!}$

where:
 * $\Si$ denotes the sine integral function
 * $x$ is a real number.