floor((log(4)/log(3))^n).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =2a(5) =3a(6) =4a(7) =5a(8) =6a(9) =8a(10) =10a(11) =12a(12) =16a(13) =20a(14) =25a(15) =32a(16) =41a(17) =52a(18) =65a(19) =83a(20) =104a(21) =132a(22) =166a(23) =210a(24) =265a(25) =335a(26) =422a(27) =533a(28) =673a(29) =849