A First Course in Modular Forms
《A First Course in Modular Forms》 · 第 19 页 · Section 1.2
The Dedekind eta function is the infinite product $\eta(\tau)=q^{1/24}\prod_{n=1}^{\infty}(1-q^n)$, where $q^{1/24}=e^{2\pi i\tau/24}$ and $q=e^{2\pi i\tau}$.