Introduction to Analytic Number Theory
《Introduction to Analytic Number Theory》 · 第 318 页 · Section 14.8「Jacobi's triple product identity」，Theorem 14.6
Jacobi's triple product identity states that, for $|x|<1$ and $z\ne0$, $\prod_{n=1}^{\infty}(1-x^{2n})(1+x^{2n-1}z^2)(1+x^{2n-1}z^{-2})=\sum_{m=-\infty}^{\infty}x^{m^2}z^{2m}$.