Introduction to Analytic Number Theory
《Introduction to Analytic Number Theory》 · 第 176 页 · Chapter 8「Some Important Functions」练习 15
The Kloosterman sum $K(m,n;k)$ is defined as follows: $K(m,n;k)=\sum_{h\bmod k,\,(h,k)=1}e^{2\pi i(mh+nh')/k}$, where $h'$ is the reciprocal of $h$ modulo $k$.