3117: Beautiful Pairs of Numbers
Description
The sequence of integer pairs (a1,b1),(a2,b2),...,(ak,bk) is beautiful, if the following statements are fulfilled:
- 1≤a1≤b1<a2≤b2<...<ak≤bk≤n, where n is a given positive integer;
- all numbers b1-a1, b2-a2, ..., bk-ak are distinct.
For the given number n find the number of beautiful sequences of length k. As the answer can be rather large, print the remainder after dividing it by 1000000007 (109+7).
The first line contains integer t (1≤t≤2·105) − the number of the test data.
Each of the next t lines contains two integers n and k (1≤k≤n≤1000).
For each test from the input print the answer to the problem modulo 1000000007 (109+7). Print the answers to the tests in the order in which the tests are given in the input.
6
1 1
2 1
2 2
3 1
3 2
3 3
1
3
0
6
2
0
In the first test sample there is exactly one beautiful sequence: (1,1).
In the second test sample, the following sequences are beautiful:
- (1,1);
- (1,2);
- (2,2).
In the fourth test sample, the following sequences are beautiful:
- (1,1);
- (1,2);
- (1,3);
- (2,2);
- (2,3);
- (3,3).
In the fifth test sample, the following sequences are beautiful:
- (1,1),(2,3);
- (1,2),(3,3).
In the third and sixth samples, there are no beautiful sequences.