Numbers whose base-4 representation has the same nonzero number of 1's and 3's.

Terms

a(0) =7a(1) =13a(2) =19a(3) =27a(4) =28a(5) =30a(6) =39a(7) =45a(8) =49a(9) =52a(10) =54a(11) =57a(12) =67a(13) =75a(14) =76a(15) =78a(16) =95a(17) =99a(18) =107a(19) =108a(20) =110a(21) =112a(22) =114a(23) =119a(24) =120a(25) =122a(26) =125a(27) =135a(28) =141a(29) =147