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A193775 Number of signed permutations invariant under the reverse complement and avoiding (-2, -1), (-1, 2), and (1, -2). 0

%I

%S 1,2,3,4,10,12,52,58,394,418

%N Number of signed permutations invariant under the reverse complement and avoiding (-2, -1), (-1, 2), and (1, -2).

%F a(n) = (\lfloor n/2\rfloor)! 2^{\lfloor n/2\rfloor} + \sum_{k=0}^{\lfloor n/2\lceil} k!

%e For n = 3, the permutations are (1, 2, 3), (3, 2, 1), (-1, -2, -3), and (-3, 2, -1).

%K nonn

%O 0,2

%A _Andy Hardt_, Aug 04 2011

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Last modified August 11 11:29 EDT 2022. Contains 356065 sequences. (Running on oeis4.)