这些东西可能不久后就会消失吧......
呵.呵.呵.呵.呵(低语的阴险.jpg)
\[n = \sum_{d|n} \varphi(d)\]
\[[n=1] = \sum_{d|n} \mu(d)\]
\[\sum_{i=1}^n i^2 = \frac{n(n+1)(2n+1)}{6}\]
\[\varphi(d) = \sum_{d|n} d\mu(\frac{n}{d})\]
\[\sum_{i=1}^n i^3 = (\sum_{i=1}^n i)^2\]
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转载自www.cnblogs.com/GuessYCB/p/9426789.html
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