A137729 Number of circular permutations of the multiset {1,1,2,2,...,n,n} (up to rotations).

1, 1, 2, 16, 318, 11352, 623760, 48648960, 5108105520, 694702028160, 118794043549440, 24946749109094400, 6311527524161798400, 1893458257242791500800, 664603848292138865510400, 269829162406607158901145600

Offset

0,3

Links

Alois P. Heinz, Table of n, a(n) for n = 0..200

Formula

a(n) = ((2*n)!/2^n + n!) / (2*n).

Crossrefs

Cf. A114938, A137730, A137737, A137749.

Row n=2 of A208183.

Sequence in context: A189189 A188867 A282787 * A278589 A171212 A385619

Adjacent sequences: A137726 A137727 A137728 * A137730 A137731 A137732

Keyword

nonn

Author

Max Alekseyev, Feb 09 2008

Extensions

a(0)=1 prepended by Alois P. Heinz, Jul 28 2015

Status

approved