https://www.luogu.com.cn/problem/P4240
欧拉函数/莫比乌斯反演
结论：
\[\varphi(ij)=\frac{\varphi(i)\varphi(j)\gcd(i,j)}{\varphi(\gcd(i,j))} \]
证明见此处
正常操作之后，得到这样一个式子
\[Ans=\sum_{T=1}^n(\sum_{d|T} \frac{d}{\varphi(d)} \mu(\frac{T}{d}))(\sum_{i=1}^{\lfloor \frac{n}{T} \rfloor } \varphi(iT))(\sum_{j=1}^{\lfloor \frac{m}{T} \rfloor } \varphi(jT))\\ 令f(n)=\sum_{d|n} \frac{d}{\varphi(d)} \mu(\frac{n}{d}),g(T,n)=\sum_{i=1}^n \varphi(iT)\\ Ans=\sum_{T=1}^n f(T)g(T,\lfloor \frac{n}{T} \rfloor)g(T,\lfloor \frac{m}{T} \rfloor) \]