id:A137737 - OEIS Search Results

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

+0
5

0, 1, 0, 30, 0, 13560, 0, 27785520, 0, 162030637440, 0, 2156625389318400, 0, 56857271240920550400, 0, 2686506065987036477184000, 0, 211180868835057744408834048000, 0, 26072812428113877344085395644416000, 0 (list; graph; listen)

	OFFSET	`1,4`
	FORMULA	`For odd n, a(n) = 0. For even n, a(n) = (n!^3 / (n/2)!^2 / 2^n + n!) / (2n).` `a(2n) = A137749(n)`
	CROSSREFS	`Cf. A114938, A137729, A137730, A137749` `Sequence in context: A022068 A030128 A137348 this_sequence A062513 A040906 A040907` `Adjacent sequences: A137734 A137735 A137736 this_sequence A137738 A137739 A137740`
	KEYWORD	`nonn`
	AUTHOR	`Max Alekseyev (maxal(AT)cs.ucsd.edu), Feb 09, 2008`

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Last modified August 29 17:54 EDT 2008. Contains 143238 sequences.

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