HDU 6750 Function（莫比乌斯反演）（2020百度之星初赛1）
Function推式子S(n)=∑i=1n∑d∣id[gcd(d,id)==1]=∑d=1nd∑d∣i[gcd(d,id)==1]=∑d=1nd∑i=1nd[gcd(d,i)==1]=∑d=1nd∑i=1nd∑k∣gcd(d,i)μ(k)=∑k=1nμ(k)k∑d=1nkd∑i=1nk2dt=k2d=∑t=1nnt∑k2∣tμ(k)ktk2=∑k=1nμ(k)k∑k2∣tnttk2i=tk2=∑k=1nμ(k)k∑i=1nk2nik2iS(n) = \sum_{i = 1} ^{n} \sum_
