A193774 Number of signed permutations of length n invariant under the reverse complement and avoiding (-2, 1) and (2, -1).

1, 2, 4, 6, 20, 26, 124, 146, 956, 1050, 9100

Offset: 0

Author

Andy Hardt, Aug 04 2011

Keywords

• nonn

Examples

			For n = 2, the permutations are (1, 2), (2, 1), (-1, -2), and (-2, -1).