如何在小于 O(n)O(\sqrt n)O(n) 的时间复杂度内求出
n≤1016n\le 10^{16}n≤1016
∑d=1n∑i=1n/d∑j=1m/d[gcd(i,j)=1]\sum_{d=1}^n \sum_{i=1}^{\sqrt {n/d}}\sum_{j=1}^{\sqrt{m/d}}[\gcd(i,j)=1]∑d=1n∑i=1n/d∑j=1m/d[gcd(i,j)=1]
