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%I #11 Aug 29 2021 01:59:30
%S 89,98,189,198,289,298,389,398,489,498,589,598,689,698,789,798,899,
%T 989,998,1089,1098,1189,1198,1289,1298,1389,1398,1489,1498,1589,1598,
%U 1689,1698,1789,1798,1899,1989,1998,2089,2098,2189
%N Numbers k such that 8 and 9 occur juxtaposed in the base-10 representation of k but not of k+1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{8,9}]>0 || SequenceCount[IntegerDigits[n],{9,8}]>0,1,0],{n,2200}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 24 2018 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_