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A193776 Number of signed permutations of length n invariant under the reverse complement and avoiding (-2, -1), (-2, 1), (2, -1). 0

%I

%S 1,2,3,5,12,17,65,80,473,527

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

%F a(2k) = 2^k k! + \sum_{j=0}^{k-1}(k-j-1)! a(2j)

%F a(2k+1) = (2^k + 1)k! + \sum_{j=0}^{k-1}(k-j-1)! a(2j+1)

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

%K nonn

%O 0,2

%A _Andy Hardt_, Aug 04 2011

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Last modified September 29 09:23 EDT 2022. Contains 357088 sequences. (Running on oeis4.)