how I can express correctely in one serie the following expresion $ $ \sum _{(k=-20) (k\neq 0)}^{20} -\frac{2 \left(\frac{3}{2} \pi \csc \left(\frac{1}{2} (2 \pi k+\pi )\right) \text{sech}\left(\frac{1}{3} \pi (2 k+1)\right)-\frac{2}{3} \pi \sec (\pi k) \text{sech}\left(\frac{3}{4} \pi (2 k+1)\right)\right)}{\pi ^2 k (2 k+1)^3}$ $ normaly I must to divide the expresion in two series from k=-infinite to -1 and for 1 to Infinity to avoid the zero thanks

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