Number of signed permutations of size 2n invariant under D and D'bar and avoiding (-2, 1) and (2, -1).

A193777

Number of signed permutations of size 2n invariant under D and D'bar and avoiding (-2, 1) and (2, -1).

Terms

    a(0) =1a(1) =2a(2) =6a(3) =18a(4) =58a(5) =190a(6) =642a(7) =2206a(8) =7746a(9) =27662a(10) =100738a(11) =373550a(12) =1413506a(13) =5457710a(14) =21546466a(15) =87025806a(16) =360264258a(17) =1529624366a(18) =6669850466a(19) =29877013902a(20) =137560725890a(21) =650780790894

External references