zhuzihan

摘要： 题目链接 推式子 \[ \sum_{i=1}^{n} \sum_{j=1}^{m} [\gcd(i,j) = d]\\ \sum_{i=1}^{\frac nd} \sum_{j=1}^{\frac md} [\gcd(i,j) = 1] \\ \\ \sum_{i=1}^{n} \sum_{j=1 阅读全文