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A137730 Number of circular permutations of the multiset {1,1,2,2,...,n,n} (up to rotations) with odd distances between equal elements. 7
1, 1, 7, 72, 1452, 43200, 1814760, 101606400, 7315680960, 658409472000, 72425043734400, 9560105533440000, 1491376463456140800, 271430516305428480000, 57000408424183569945600, 13680098021793595392000000, 3720986661927868408018944000, 1138621918549924531666944000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..18.

FORMULA

For even n, a(n) = n!^2 / (2n). For odd n, a(n) = (n!^2 + n!) / (2n).

CROSSREFS

Cf. A114938, A137729, A137737, A137749.

Sequence in context: A203473 A197951 A221161 * A157920 A321077 A080794

Adjacent sequences:  A137727 A137728 A137729 * A137731 A137732 A137733

KEYWORD

nonn

AUTHOR

Max Alekseyev, Feb 09, 2008

STATUS

approved

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Last modified November 27 16:35 EST 2021. Contains 349394 sequences. (Running on oeis4.)