Hamming weight of 3n: number of 1's in binary expansion of 3n.

Terms

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