Numbers whose base-4 representation has the same number of 1's and 2's.

Terms

a(0) =0a(1) =3a(2) =6a(3) =9a(4) =12a(5) =15a(6) =18a(7) =24a(8) =27a(9) =30a(10) =33a(11) =36a(12) =39a(13) =45a(14) =48a(15) =51a(16) =54a(17) =57a(18) =60a(19) =63a(20) =66a(21) =72a(22) =75a(23) =78a(24) =90a(25) =96a(26) =99a(27) =102a(28) =105a(29) =108