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http://www.lydsy.com/JudgeOnline/problem.php?id=2693 阅读全文
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http://www.lydsy.com/JudgeOnline/problem.php?id=4916 阅读全文
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BZOJ 4176 http://www.lydsy.com/JudgeOnline/problem.php?id=4176 莫比乌斯反演+杜教筛 好像μ可以杜教筛肛 s可以有√n的做法 复杂度为 BZOJ3994 http://www.lydsy.com/JudgeOnline/problem.p 阅读全文
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https://www.51nod.com/onlineJudge/questionCode.html#!problemId=1239 51nod 1239 欧拉函数之和 https://www.51nod.com/onlineJudge/questionCode.html#!problemId=1 阅读全文
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http://www.lydsy.com/JudgeOnline/problem.php?id=4407 阅读全文
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http://www.lydsy.com/JudgeOnline/problem.php?id=4804 可以反演成Σ(i=1,n)(Σ(j,j|i)μ(j)*Φ(i/j))*[n/i]*[n/i] 过程略 设f(i)=Σ(j,j|i)μ(j)*Φ(i/j) f就是μ和Φ的卷积 μ,Φ都是积性函数 阅读全文
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http://www.lydsy.com/JudgeOnline/problem.php?id=2820 首先按照套路 ans =ΣprimeΣ(i=1,n)Σ(j=1,m)[gcd(i,j)=prime] =ΣprimeΣ(i=1,[n/prime])Σ(j=1,[m/prime])[gcd(i, 阅读全文
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BZOJ1101 http://www.lydsy.com/JudgeOnline/problem.php?id=1101 求gcd(a,b)=k a,b中必然包含k的因子 问题等价于a'=a/k,b'=b/k,求有多少对(i,j),其gcd(i,j)=1,1<=i<=a',1<=j<=b' ans 阅读全文