walfy

摘要： $F(n)=\sum_{i=1}^n\sum_{j=1}^n[lcm(i,j)+gcd(i,j)\geq n]$ $S(n)=\sum_{i=1}^nF(i)$ $F(n)=n^2 \sum_{i=1}^n\sum_{j=1}^n[lcm(i,j)+gcd(i,j) // include defin 阅读全文