a(n) = a(n-1) + a(n-2) + 1, with a(0) = 0, a(1) = 9.

Terms

a(0) =0a(1) =9a(2) =10a(3) =20a(4) =31a(5) =52a(6) =84a(7) =137a(8) =222a(9) =360a(10) =583a(11) =944a(12) =1528a(13) =2473a(14) =4002a(15) =6476a(16) =10479a(17) =16956a(18) =27436a(19) =44393a(20) =71830a(21) =116224a(22) =188055a(23) =304280a(24) =492336a(25) =796617a(26) =1288954a(27) =2085572a(28) =3374527a(29) =5460100