∑i=1n∑j=1n/i∑k=1n/(ij)[i∗j∗k<n]\sum_{i=1}^n\sum_{j=1}^{n/i}\sum_{k=1}^{n/(ij)}[i*j*k<n]∑i=1n∑j=1n/i∑k=1n/(ij)[i∗j∗k<n]
