数学草稿
P13645 Totient with Divisors
\[\begin{aligned}\sum_{i=1}^n\sum_{j=1}^m\varphi(i)\varphi(j)\sigma(ij)&=\sum_{i=1}^n\sum_{j=1}^m\varphi(i)\varphi(j)\sum_{a|i}\sum_{b|j}\frac{ib}{a}\times[a\perp b]\\&=\sum_{o=1}^{n}\mu(o) ...
穆望
2025-11-22 20:02
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