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%I #15 Feb 18 2021 11:33:31
%S 91,191,291,391,491,591,691,791,891,919,991,1091,1191,1291,1391,1491,
%T 1591,1691,1791,1891,1919,1991,2091,2191,2291,2391,2491,2591,2691,
%U 2791,2891,2919,2991,3091,3191,3291,3391,3491,3591,3691,3791,3891,3919,3991,4091,4191
%N Numbers m such that string 9,1 occurs in the base 10 representation of m but not of m+1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{9,1}]>0,1,0],{n,4000}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Dec 14 2019 *)
%o (PARI) isok(m) = (#strsplit(Str(m), "91") > 1) && (#strsplit(Str(m+1), "91") == 1); \\ _Michel Marcus_, Feb 18 2021
%K nonn,base
%O 1,1
%A _Clark Kimberling_
%E Conjecture on linear recurrence removed by _Georg Fischer_, Feb 18 2021
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