小x的奇遇-adventure 题意: 给定函数f(n),g(n),求 G k ( n ) G_k(n) Gk(n) f ( n ) = { 1 , n = 1 ∑ i = 1 n − 1 [ g c d ( i , n − i ) = = 1 ] , n > 1 f(n)=\begin{cases} 1,n=1\\ \sum_{i=1}^{n-1}[gcd(i,n-i)==1],n>1 \end{cases} f(n)={ 1,n=1∑i=1n−1[gcd(i,n−i)==1],n>1 g ( n ) = ∑ d ∣ n f ( n d ) ...