摘要： 题意 求： \[\sum_{i = 1} ^ n \sum_{j = 1} ^ m [\gcd(i, j) \in prime] \]Sol 考虑先枚举 \(gcd\) \[\sum_{k = 1} ^ {\min(n, m)} \sum_{i = 1} ^ n \sum_{j = 1} ^ m [ 阅读全文