Number of ways to tile a "central bump" strip of length n with 1 X 1 squares and 1 X 3 rectangles.

Terms

a(0) =4a(1) =9a(2) =13a(3) =25a(4) =30a(5) =35a(6) =52a(7) =78a(8) =121a(9) =189a(10) =271a(11) =388a(12) =561a(13) =812a(14) =1204a(15) =1785a(16) =2617a(17) =3837a(18) =5602a(19) =8179a(20) =12000a(21) =17606a(22) =25825a(23) =37881a(24) =55483a(25) =81264a(26) =119089a(27) =174520a(28) =255828a(29) =375017