tata_d2的博客

「SDOI2014」数表设σ(x)σ(x)\sigma(x)为xxx的约束和，求 ∑i=1n∑j=1m∑k=1ak[σ(gcd(i,j))=k]∑i=1n∑j=1m∑k=1ak[σ(gcd(i,j))=k]\sum_{i=1}^n \sum_{j=1}^m \sum_{k=1}^a k[\sigma(gcd(i, j)) = k] 数据组数<=20000<=20000 n,m...

「CQOI2015」选数

杜教筛求积性函数f(x)f(x)f(x)的前缀和S(n)=∑ni=1f(i)S(n)=∑i=1nf(i)S(n) = \sum_{i=1}^n f(i)狄利克雷卷积： (g∗f)(x)=∑d|xg(d)f(xd)(g∗f)(x)=∑d|xg(d)f(xd)(g*f)(x) = \sum_{d|x} g(d) f(\dfrac{x}{d})∑x=1n(g∗f)(x)=∑x=1n∑d|x...

51nod 1222求满足a≤lcm(i,j)≤ba≤lcm(i,j)≤b a \leq lcm(i, j) \leq b 的二元组[i,j][i,j][i, j]的个数a,b≤1011a,b≤1011a, b \leq 10^{11}设S(n)=∑i=1n∑j=1i[ijgcd(i,j)≤n]S(n)=∑i=1n∑j=1i[ijgcd(i,j)≤n]S(n) = \sum_{...

求 ∑i=1n∑j=1nij gcd(i,j)∑i=1n∑j=1nij gcd(i,j)\sum_{i=1}^n \sum_{j=1}^n ij \ gcd(i, j) n≤1010n≤1010n \leq 10^{10}ans=∑d=1nd∑i=1n∑j=1nij [gcd(i,j)=d]ans=∑d=1nd∑i=1n∑j=1nij [gcd...