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

Terms

a(0) =2a(1) =3a(2) =4a(3) =10a(4) =11a(5) =14a(6) =15a(7) =18a(8) =19a(9) =24a(10) =28a(11) =33a(12) =36a(13) =42a(14) =43a(15) =46a(16) =47a(17) =49a(18) =52a(19) =58a(20) =59a(21) =62a(22) =63a(23) =65a(24) =68a(25) =74a(26) =75a(27) =78a(28) =79a(29) =80