a(n) = Sum_{k=1..n} floor(3*n/3^k).

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =5a(5) =6a(6) =8a(7) =9a(8) =10a(9) =13a(10) =14a(11) =15a(12) =17a(13) =18a(14) =19a(15) =21a(16) =22a(17) =23a(18) =26a(19) =27a(20) =28a(21) =30a(22) =31a(23) =32a(24) =34a(25) =35a(26) =36a(27) =40a(28) =41a(29) =42