1013: 湖南省第十七届大学生计算机程序设计竞赛（HNCPC2021） - Semilive
Start Time：2021-12-05 18:00:00 End Time：2021-12-05 23:00:00 Current Time：2025-07-04 15:23:13 Public Ended
D (1160) : Sum Them
Time Limit: 1 Sec Memory Limit: 128 MB Submitted: 130 Solved: 34Description
Given n and m, calculate the sum of the incremental multiplication formulas:
$$ f(n, m)=\sum_{i=1}^{n}\prod_{j=i}^{i+m-1}j $$
Input
No more than 50 test cases. Each case one line, including integer n and m.
1 ≤ n, m ≤ 106.
Output
For each test case, output the result of f(n, m) modulo 109 + 7.
Sample
2 2 98 3
8 24497550