k-1-n-1-2k-2n-k-

Question Number 160160 by cortano last updated on 25/Nov/21

$$\:\:\:\:\underset{{k}=\mathrm{1}} {\overset{{n}} {\sum}}\:\frac{\mathrm{1}}{\left(\mathrm{2}{k}\right)!\left(\mathrm{2}{n}−{k}\right)!}=? \\ $$