Score : 600 points
Let us define the oddness of a permutation p = {p_1,\ p_2,\ ...,\ p_n} of {1,\ 2,\ ...,\ n} as \sum_{i = 1}^n |i - p_i|.
Find the number of permutations of {1,\ 2,\ ...,\ n} of oddness k, modulo 10^9+7.
Input is given from Standard Input in the following format:
n k
Print the number of permutations of {1,\ 2,\ ...,\ n} of oddness k, modulo 10^9+7.
3 2
2
There are six permutations of {1,\ 2,\ 3}. Among them, two have oddness of 2: {2,\ 1,\ 3} and {1,\ 3,\ 2}.
39 14
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