sum_(k=-∞)^∞ sum_(j=-∞)^∞( piecewise | (j + k τ)^(-2 n) | j^2 + k^2!=0 0 | otherwise) = 2 ζ(2 n) + (( sum_(k=1)^∞ σ_(2 n - 1)(k) e^(2 π i k τ)) (2 (2 π i)^(2 n)))/((2 n - 1)!) for (n element Z and n>1)