Base 4 expansion uses each positive digit just once.

Terms

a(0) =27a(1) =30a(2) =39a(3) =45a(4) =54a(5) =57a(6) =75a(7) =78a(8) =99a(9) =108a(10) =114a(11) =120a(12) =135a(13) =141a(14) =147a(15) =156a(16) =177a(17) =180a(18) =198a(19) =201a(20) =210a(21) =216a(22) =225a(23) =228a(24) =267a(25) =270a(26) =291a(27) =300a(28) =306a(29) =312