Numbers k such that 1 and 9 occur juxtaposed in the base-10 representation of k but not of k-1.

Terms

a(0) =19a(1) =91a(2) =119a(3) =190a(4) =219a(5) =291a(6) =319a(7) =391a(8) =419a(9) =491a(10) =519a(11) =591a(12) =619a(13) =691a(14) =719a(15) =791a(16) =819a(17) =891a(18) =910a(19) =991a(20) =1019a(21) =1091a(22) =1119a(23) =1190a(24) =1219a(25) =1291a(26) =1319a(27) =1391a(28) =1419a(29) =1491