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Numbers k such that 0 and 9 occur juxtaposed in the base-10 representation of k but not of k+1.
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%I #11 Aug 27 2021 08:27:41

%S 90,109,190,209,290,309,390,409,490,509,590,609,690,709,790,809,890,

%T 909,990,1009,1099,1109,1190,1209,1290,1309,1390,1409,1490,1509,1590,

%U 1609,1690,1709,1790,1809,1890,1909,1990,2009,2099

%N Numbers k such that 0 and 9 occur juxtaposed in the base-10 representation of k but not of k+1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{0,9}]>0 || SequenceCount[ IntegerDigits[n],{9,0}]>0,1,0],{n,2200}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 28 2021 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_