Question Number 133344 by Dwaipayan Shikari last updated on 21/Feb/21
$$\underset{{n}=\mathrm{1}} {\overset{\infty} {\sum}}\frac{{cos}\left(\frac{{n}}{\pi}\right)}{{n}^{\mathrm{4}} }=−\frac{\mathrm{1}}{\mathrm{48}\pi^{\mathrm{4}} }+\frac{\mathrm{1}}{\mathrm{12}}\left(\mathrm{1}−\frac{\mathrm{1}}{\pi^{\mathrm{2}} }\right)+\frac{\pi^{\mathrm{4}} }{\mathrm{90}} \\ $$