摘要：
"http://www.51nod.com/onlineJudge/questionCode.html !problemId=1238" 设$A(n)=\sum\limits_{i=1}^n\frac{in}{(i,n)}$，则$ans=\sum\limits_{i=1}^n\left(2A(i) 阅读全文
摘要：
"http://www.51nod.com/onlineJudge/questionCode.html !problemId=1190" $$ \begin{aligned} &\sum_{i=a}^b\frac{ib}{(i,b)}\\ =&b\sum_{i=a}^b\frac i{(i,b)}\ 阅读全文