摘要:
\[ ans=\sum_{i=1}^n\sum_{j=1}^n(i+j)^kf(gcd(i,j))gcd(i,j) \] \[ \begin{aligned} ans & =\sum_{i=1}^n\sum_{j=1}^n(i+j)^kf(gcd(i,j))gcd(i,j) \\ & =\sum_{ 阅读全文
posted @ 2020-08-25 16:05
starseven
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摘要:
\[ ans=\sum_{i=1}^nlcm(i,n) \] \[ \begin{aligned} ans & =\sum_{i=1}^nlcm(i,n) \\ & =\sum_{i=1}^n\frac{i\cdot n}{gcd(i,n)} \\ & =n\times \sum_{i=1}^n\f 阅读全文
posted @ 2020-08-25 16:04
starseven
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