%I #7 Jul 27 2020 18:16:11
%S 31,80,129,178,223,227,276,325,374,423,472,521,566,570,619,668,717,
%T 766,815,864,909,913,962,1011,1060,1109,1158,1207,1252,1256,1305,1354,
%U 1403,1452,1501,1567,1595,1599,1648,1697,1746,1795
%N Numbers n such that string 4,3 occurs in the base 7 representation of n but not of n+1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,7],{4,3}]>0,1,0],{n,2000}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jul 27 2020 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_