Question Number 139359 by Dwaipayan Shikari last updated on 26/Apr/21
$$\underset{{n}=\mathrm{0}} {\overset{\infty} {\sum}}\frac{\mathrm{1}}{\left(\mathrm{6}{n}\right)!} \\ $$
Commented by Dwaipayan Shikari last updated on 28/Apr/21
$$\frac{{cosh}\left(\mathrm{1}\right)+\mathrm{2}{cosh}\left(\frac{\mathrm{1}}{\mathrm{2}}\right){cos}\left(\frac{\sqrt{\mathrm{3}}}{\mathrm{2}}\right)}{\mathrm{3}} \\ $$