Sum over k of Stirling Numbers of Second Kind by x^k

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Theorem

\(\ds \sum_k {k \brace n} z^k\) \(=\) \(\ds \dfrac {z^n} {\prod \limits_{k \mathop = 1}^n \paren {1 - k n} }\)
\(\ds \) \(=\) \(\ds \dfrac {z^n} {\paren {1 - z} \paren {1 - 2 z} \cdots \paren {1 - n z} }\)

where:

$\ds {k \brace n}$ denotes a Stirling number of the second kind.


Proof




Sources