a(n) = (1/3)*s(n), where s(n) is the n-th multiple of 3 in A026136.

Terms

a(0) =1a(1) =3a(2) =5a(3) =2a(4) =7a(5) =9a(6) =11a(7) =4a(8) =13a(9) =15a(10) =17a(11) =6a(12) =19a(13) =21a(14) =23a(15) =8a(16) =25a(17) =27a(18) =29a(19) =10a(20) =31a(21) =33a(22) =35a(23) =12a(24) =37a(25) =39a(26) =41a(27) =14a(28) =43a(29) =45