Number of reversible strings with n beads of 2 colors. If more than 1 bead, not palindromic.

Terms

a(0) =2a(1) =1a(2) =2a(3) =6a(4) =12a(5) =28a(6) =56a(7) =120a(8) =240a(9) =496a(10) =992a(11) =2016a(12) =4032a(13) =8128a(14) =16256a(15) =32640a(16) =65280a(17) =130816a(18) =261632a(19) =523776a(20) =1047552a(21) =2096128a(22) =4192256a(23) =8386560a(24) =16773120a(25) =33550336a(26) =67100672a(27) =134209536a(28) =268419072a(29) =536854528