# Power of Complex Number as Summation of Stirling Numbers of Second Kind

## Theorem

Let $z \in \C$ be a complex number whose real part is positive.

Then:

$z^r = \displaystyle \sum_{k \mathop \in \Z} {r \brace r - k} z^{\underline {r - k} }$

where:

$\displaystyle {r \brace r - k}$ denotes the extension of the Stirling numbers of the second kind to the complex plane
$z^{\underline {r - k} }$ denotes $z$ to the $r - k$ falling.

## Historical Note

Donald E. Knuth acknowledges the work of Benjamin Franklin Logan in his The Art of Computer Programming: Volume 1: Fundamental Algorithms, 3rd ed. of $1997$.