Number of n X n matrices with exactly 2 1's in each row and column, other entries 0.
1, 0, 1, 6, 90, 2040, 67950, 3110940, 187530840, 14398171200, 1371785398200
1 seqfan posts
Sun Jan 18 02:59:08 CET 2009 [seqfan] Re: Two Sequences Related To Permutations of (1,2,...,n)