a(n) = floor((4/3)^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =3a(5) =4a(6) =5a(7) =7a(8) =9a(9) =13a(10) =17a(11) =23a(12) =31a(13) =42a(14) =56a(15) =74a(16) =99a(17) =133a(18) =177a(19) =236a(20) =315a(21) =420a(22) =560a(23) =747a(24) =996a(25) =1328a(26) =1771a(27) =2362a(28) =3149a(29) =4199