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Numbers n such that string 1,5 occurs in the base 7 representation of n but not of n-1.
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%I #7 Jan 16 2015 15:22:30

%S 12,61,84,110,159,208,257,306,355,404,427,453,502,551,588,649,698,747,

%T 770,796,845,894,943,992,1041,1090,1113,1139,1188,1237,1286,1335,1384,

%U 1433,1456,1482,1531,1580,1629,1678,1727,1776

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

%t Flatten[Position[Partition[Table[If[MemberQ[Partition[IntegerDigits[n,7],2,1],{1,5}],1,0],{n,2000}],2,1],{0,1}]]+1 (* _Harvey P. Dale_, Jan 16 2015 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_