CitadelOA #10
Checksum Aggregation
估计困难可在线判题
考点(AI 标注)位运算
Packets are numbered 1..n, and C(i,j)=i mod j+j mod i. Find the sum of C over all ordered pairs modulo 1000000007. The diagonal terms are 0, so it makes no difference whether the pairs must consist of distinct packets.
输入格式
One line containing n; complete OCR bound 1≤n≤1000000.
输出格式
Output a single integer, the answer.
样例 1
输入:
2
输出:
2
样例 2
输入:
3
输出:
10
样例 3
输入:
4
输出:
24
样例说明
The outputs of the three public examples are, in order: 2; 10; 24. These answers were verified by independent enumeration or direct simulation.