Number of non-alternating compositions of n, excluding twins (x,x).

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =3a(5) =9a(6) =19a(7) =45a(8) =98a(9) =208a(10) =436a(11) =906a(12) =1861a(13) =3803a(14) =7731a(15) =15659a(16) =31628a(17) =63747a(18) =128257a(19) =257722a(20) =517338a(21) =1037652a(22) =2079983a(23) =4167325a(24) =8346203a(25) =16710572a(26) =33449694a(27) =66944254a(28) =133959020a(29) =268028868