摘要：$$\begin{eqnarray}&\sum_{i=1}^{n}\sum_{j=1}^{n}ij\gcd(i,j)\\&\sum_{d=1}^{n}\sum_{i=1}^{n}\sum_{j=1}^{n}ij[\gcd(i,j)=d] \\&\sum_{d=1}^{n}d^3\sum_{i=1}^ 阅读全文