Numbers whose base-10 representation has the same nonzero number of 1's and 9's.

Terms

a(0) =19a(1) =91a(2) =109a(3) =129a(4) =139a(5) =149a(6) =159a(7) =169a(8) =179a(9) =189a(10) =190a(11) =192a(12) =193a(13) =194a(14) =195a(15) =196a(16) =197a(17) =198a(18) =219a(19) =291a(20) =319a(21) =391a(22) =419a(23) =491a(24) =519a(25) =591a(26) =619a(27) =691a(28) =719a(29) =791