P2303 [SDOI2012] Longge 的问题（欧拉函数)

P2303 [SDOI2012] Longge 的问题（欧拉函数) 传送门html g ( n ) = ∑ i = 1 n g c d ( i , n ) = ∑ d ∣ n d × φ ( n d ) = ∑ d ∣ n n d φ ( d ) g(n)=\sum\limits_{i=1}^n gcd(i,n)=\sum_{d|n}d\times \varphi(\dfrac{n}{d})=\s

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