I would like to evaluate the infinite sum $$\sum_n \exp \left( \frac{i\pi}{a} (n-x)^2\right)$$ where $x,a\in \mathbb R$.
For certain values of $a$ it becomes a Delta comb of various frequencies, however I can't figure out a general expression
2026-03-29 11:00:45.1774782045
Infinite sum over $e^{i \frac{\pi (n-x)^2}{a}}$
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