Numbers whose base-4 representation has the same nonzero number of 0's and 3's.

Terms

a(0) =12a(1) =19a(2) =28a(3) =35a(4) =44a(5) =49a(6) =50a(7) =52a(8) =56a(9) =71a(10) =75a(11) =77a(12) =78a(13) =83a(14) =92a(15) =99a(16) =108a(17) =113a(18) =114a(19) =116a(20) =120a(21) =135a(22) =139a(23) =141a(24) =142a(25) =147a(26) =156a(27) =163a(28) =172a(29) =177