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

摘要：$$\begin{eqnarray}&c[k] = \sum_{i}^{n}a[i]b[i-k] \\&c[k] = \sum_{i}^{n}a[n-i]b[i-k] (倒序保存a) \\&c[n-k]= \sum_{i}^{n}a[n-i]b[i-k] (倒序保存c) \\&通过卷积 o (nlo 阅读全文