https://s0.wp.com/latex.php?latex=%5Cdisplaystyle+V+%3D+%5Cpi+%5Csum_%7Bn%3D1%7D%5E%7B%5Cinfty%7D+%5Cfrac%7B1%7D%7Bn%5E2%7D%5Ctimes+1+&bg=ffffff&fg=000000&s=0