HDU6760 Math is Simple 數學變形+莫比烏斯反演

題目描述 求 ∑ 1 ≤ a ≤ b ≤ n , g c d ( a , b ) = 1 , a + b ≥ n 1 a b \sum\limits_{1\leq a \le b \leq n,gcd(a,b)=1,a+b \geq n}\frac{1}{ab} 1≤a≤b≤n,gcd(a,b)=1,a+b≥n∑​ab1​ 1 ≤ T ≤ 1 e 4 , 1 ≤ N ≤ 1 e 8 1 \leq

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