Number of self-inverse permutations p on [n] where the maximal displacement of an element equals 2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =3a(5) =7a(6) =16a(7) =35a(8) =74a(9) =153a(10) =312a(11) =629a(12) =1257a(13) =2495a(14) =4926a(15) =9684a(16) =18972a(17) =37064a(18) =72243a(19) =140547a(20) =273007a(21) =529626a(22) =1026369a(23) =1987260a(24) =3844919a(25) =7434542a(26) =14368115a(27) =27756229a(28) =53600223a(29) =103476920