摘要：
题意:求$F(b) F(a 1),F(n)=\sum_{i=1}^n\sum_{j=1}^i\frac{i}{(i,j)}$ 题解:先枚举gcd,$=\sum_{d=1}^n\sum_{i=1}^{\lfloor \frac{n}{d} \rfloor}\sum_{j=1}^i j[gcd(i,j) 阅读全文
摘要：
题意:$\sum_{i=1}^n\sum_{j=1}^ngcd(i,j)$ 题解:先枚举gcd,$\sum_{d=1}^n\sum_{i=1}^{\lfloor \frac{n}{d} \rfloor}\sum_{j=1}^{\lfloor \frac{n}{d} \rfloor}[(i,j)=1] 阅读全文
摘要：
题意:求$\sum_{i=1}^n\sum_{j=1}^n\frac{i j}{gcd(i,j)}$ 题解:先枚举gcd,$\sum_{d=1}^nd\sum_{i=1}^{\lfloor \frac{n}{d} \rfloor}\sum_{j=1}^{\lfloor \frac{n}{d} \rf 阅读全文