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A001499 Number of n X n matrices with exactly 2 1's in each row and column, other entries 0.
(Formerly M4286 N1792)
+0
11
1, 0, 1, 6, 90, 2040, 67950, 3110940, 187530840, 14398171200, 1371785398200, 158815387962000, 21959547410077200, 3574340599104475200, 676508133623135814000, 147320988741542099484000, 36574751938491748341360000, 10268902998771351157327104000 (list; graph; listen)
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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.


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