2020杭电多校第六场 A Very Easy Math Problem 莫比乌斯反演 (HDU 6833)
AVeryEasyMathProblem题解∑a1=1n∑a2=1n⋅⋅⋅∑ax=1n(∏j=1xajk)f(gcd(a1,a2,...,an))gcd(a1,a2,...,an)=∑d=1ndf(d)∑a1=1n∑a2=1n⋅⋅⋅∑ax=1n(∏j=1xajk)[gcd(a1,a2,...,an)=d]=∑d=1ndkx+1f(d)∑a1=1⌊n/d⌋∑a2=1⌊n/d⌋⋅⋅⋅∑ax=1⌊n/d