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Numbers n such that string 4,5 occurs in the base 7 representation of n but not of n-1.
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%I #7 Feb 14 2017 12:13:17

%S 33,82,131,180,229,231,278,327,376,425,474,523,572,574,621,670,719,

%T 768,817,866,915,917,964,1013,1062,1111,1160,1209,1258,1260,1307,1356,

%U 1405,1454,1503,1552,1601,1603,1617,1699,1748,1797

%N Numbers n such that string 4,5 occurs in the base 7 representation of n but not of n-1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,7],{4,5}]>0,1,0],{n,2000}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Feb 14 2017 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_