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

Author

Max Alekseyev, Feb 09 2008

Keywords

• nonn

Links

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

Crossrefs

Cf. A114938, A137730, A137737, A137749.

Row n=2 of A208183.

Formula

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

Extensions

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