Sum over k of Unsigned Stirling Numbers of First Kind by x^k

Theorem

 * $\displaystyle \sum_k \left[{n \atop k}\right] x^k = x^{\overline n}$

where:
 * $\displaystyle \left[{n \atop k}\right]$ denotes an unsigned Stirling number of the first kind
 * $x^{\overline n}$ denotes $x$ to the $n$ rising.