摘要：\(\sum_{i=1}^A\sum_{j=1}^B\sum_{k=1}^Cd(ijk)\) \(\sum_{i=1}^A\sum_{j=1}^B\sum_{k=1}^C\sum_{x|i}\sum_{y|j}\sum_{z|k}[(x,y)=1][(y,z)=1][(x,z)=1]\) \(\su 阅读全文