a(n) = 2*a(n-1) - [(n+1)/3] for n>0 with a(0) = 1.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =9a(5) =16a(6) =30a(7) =58a(8) =113a(9) =223a(10) =443a(11) =882a(12) =1760a(13) =3516a(14) =7027a(15) =14049a(16) =28093a(17) =56180a(18) =112354a(19) =224702a(20) =449397a(21) =898787a(22) =1797567a(23) =3595126a(24) =7190244a(25) =14380480a(26) =28760951a(27) =57521893a(28) =115043777a(29) =230087544