FortinetOA #2
Checksum Aggregator
估计困难可在线判题
考点(AI 标注)位运算
Over all ordered index pairs with 1≤i,j≤n, sum C(i,j)=i mod j+j mod i, modulo 1,000,000,007. The statement requires the two indices to be distinct; diagonal terms are zero.
输入格式
A single integer n (1≤n≤1000000).
输出格式
Output the sum of the checksum over all distinct ordered pairs, modulo 1000000007.
样例 1
输入:
1
输出:
0
样例 2
输入:
2
输出:
2
样例 3
输入:
3
输出:
10
样例说明
For each fixed j, split the remainders over 1..n into complete periods and a tail.