Number of alternating compositions of n, including twins (x,x).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =5a(5) =7a(6) =13a(7) =19a(8) =30a(9) =48a(10) =76a(11) =118a(12) =187a(13) =293a(14) =461a(15) =725a(16) =1140a(17) =1789a(18) =2815a(19) =4422a(20) =6950a(21) =10924a(22) =17169a(23) =26979a(24) =42405a(25) =66644a(26) =104738a(27) =164610a(28) =258708a(29) =406588