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Q: Is it possible to calculate the integral $$ \int\limits_0^\infty \int\limits_0^\infty\frac{\cos\frac{\pi}2 \left(nx^2-\frac{y^2}n\right)\cos \pi xy}{\cosh \pi x\cosh \pi y}dxdy,~n\in\mathbb{N}\tag{1} $$ using residue theory?

For example, when $n=3$ $$ \int\limits_0^\infty \int\limits_0^\infty\frac{\cos\frac{\pi}{2} \left(3x^2-\frac{y^2}{3}\right)\cos \pi xy}{\cosh \pi x\cosh \pi y}dxdy=\frac{\sqrt{3}-1}{2\sqrt{6}}. $$ There is a closed form formula to calculate (1) for arbitrary natural $n$, but I don't know how to do it by residue theory. Maybe it is possible in principle, but is residue theory practical in this particular case? It seems such an approach would lead to a sum with $O(n^2)$ terms. Any hints would be appreciated.

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    can you give a reference for the amazing formula $n=3$? i bet it is due to ramanujan2017-01-19
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    @tired it is not due to Ramanujan.2017-01-19
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    thx, that is cool stuff...are do you doing this on a recreational basis or is this for professional purposes?2017-01-19
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    @ Nemo: would you mind if I can offer a bounty for this question?2017-10-11
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    @ Nemo:Based on residue theory.Unfortunately my browser can't display the formulas in your blog2017-10-11
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    @Nicco I don't mind2017-10-11

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