Question Number 221382 by MrGaster last updated on 02/Jun/25
$$\underset{{k}=\mathrm{0}} {\overset{{n}} {\sum}}\begin{pmatrix}{{n}}\\{{k}}\end{pmatrix}^{−\mathrm{1}} \\ $$
Commented by mr W last updated on 05/Jun/25
$$=\frac{\mathrm{1}}{{n}!}\underset{{k}=\mathrm{0}} {\overset{{n}} {\sum}}{k}!\left({n}−{k}\right)! \\ $$