Number of self-inverse permutations p on [n] where the maximal displacement of an element equals 4.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =4a(6) =18a(7) =55a(8) =151a(9) =399a(10) =1061a(11) =2792a(12) =7252a(13) =18572a(14) =47051a(15) =118291a(16) =295718a(17) =735776a(18) =1823183a(19) =4501151a(20) =11077398a(21) =27187053a(22) =66567357a(23) =162655518a(24) =396728446a(25) =966109074a(26) =2349342360a(27) =5705883591a(28) =13842565488a(29) =33549053111