a(n) = Sum_{i=1..n} floor((3/2)^i).

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =18a(5) =29a(6) =46a(7) =71a(8) =109a(9) =166a(10) =252a(11) =381a(12) =575a(13) =866a(14) =1303a(15) =1959a(16) =2944a(17) =4421a(18) =6637a(19) =9962a(20) =14949a(21) =22430a(22) =33652a(23) =50486a(24) =75737a(25) =113613a(26) =170428a(27) =255650a(28) =383484a(29) =575235