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A193774
Number of signed permutations of length n invariant under the reverse complement and avoiding (-2, 1) and (2, -1).
0
1, 2, 4, 6, 20, 26, 124, 146, 956, 1050, 9100
OFFSET
0,2
EXAMPLE
For n = 2, the permutations are (1, 2), (2, 1), (-1, -2), and (-2, -1).
CROSSREFS
Sequence in context: A279188 A108439 A245766 * A241210 A333992 A176652
KEYWORD
nonn
AUTHOR
Andy Hardt, Aug 04 2011
STATUS
approved