id:A137749 - OEIS Search Results

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Number of circular permutations of the multiset {1,1,2,2,...,2n,2n} (up to rotations) with even distances between equal elements.

+0
5

1, 30, 13560, 27785520, 162030637440, 2156625389318400, 56857271240920550400, 2686506065987036477184000, 211180868835057744408834048000, 26072812428113877344085395644416000, 4829206317935252350431489703482654720000 (list; graph; listen)

	OFFSET	`1,2`
	FORMULA	`a(n) = ((2n)!^3 / n!^2 / 2^(2n) + (2n)!) / (4n).` `a(n) = A137737(2n)`
	CROSSREFS	`Cf. A114938, A137729, A137730, A137737` `Sequence in context: A087216 A059049 A056071 this_sequence A007741 A089037 A116076` `Adjacent sequences: A137746 A137747 A137748 this_sequence A137750 A137751 A137752`
	KEYWORD	`nonn`
	AUTHOR	`Max Alekseyev (maxale(AT)gmail.com), Feb 09, 2008`

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Last modified December 21 10:15 EST 2009. Contains 171081 sequences.

AT&T Labs Research