A073584 Commuting even permutations: number of ordered pairs g, h in the alternating group A_n such that gh = hg.

1, 1, 9, 48, 300, 2520, 22680, 282240, 3265920, 43545600, 618710400, 10298534400, 171243072000, 3138418483200, 61460695296000, 1286751578112000, 27743619391488000, 640237370572800000, 15448927751921664000, 394130125324615680000, 10422552203028725760000, 288306186674956369920000

Offset

1,3

Links

N. J. A. Sloane, Table of n, a(n) for n = 1..37

Formula

For n>=2 : a(n) = (n!/2) * A000702(n).

Crossrefs

Cf. A000702, A053529.

Sequence in context: A171011 A264273 A226751 * A007037 A179280 A293095

Adjacent sequences: A073581 A073582 A073583 * A073585 A073586 A073587

Keyword

nonn

Author

Yuval Dekel (dekelyuval(AT)hotmail.com), Sep 13 2003

Extensions

More terms from N. J. A. Sloane (based on A000720), Dec 31 2006

Status

approved