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

Terms

a(0) =4a(1) =18a(2) =19a(3) =24a(4) =28a(5) =33a(6) =36a(7) =49a(8) =52a(9) =65a(10) =68a(11) =74a(12) =75a(13) =78a(14) =79a(15) =80a(16) =98a(17) =99a(18) =104a(19) =108a(20) =114a(21) =115a(22) =120a(23) =124a(24) =134a(25) =135a(26) =137a(27) =141a(28) =146a(29) =147