Numbers whose base-4 representation has the same number of 0's, 1's and 2's.

Terms

a(0) =3a(1) =15a(2) =18a(3) =24a(4) =33a(5) =36a(6) =63a(7) =75a(8) =78a(9) =99a(10) =108a(11) =114a(12) =120a(13) =135a(14) =141a(15) =147a(16) =156a(17) =177a(18) =180a(19) =198a(20) =201a(21) =210a(22) =216a(23) =225a(24) =228a(25) =255a(26) =303a(27) =315a(28) =318a(29) =399