%I #9 Nov 19 2023 12:08:55

%S 41,90,139,188,237,293,335,384,433,482,531,580,636,678,727,776,825,

%T 874,923,979,1021,1070,1119,1168,1217,1266,1322,1364,1413,1462,1511,

%U 1560,1609,1665,1707,1756,1805,1854,1903,1952,2057

%N Numbers k such that string 5,6 occurs in the base 7 representation of k but not of k+1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,7],{5,6}]>0,1,0],{n,2100}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 21 2017 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_