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%I #8 Dec 31 2017 13:45:24
%S 55,119,183,247,311,375,439,503,567,631,695,759,823,887,951,1015,1079,
%T 1143,1207,1271,1335,1399,1463,1527,1591,1655,1719,1783,1847,1911,
%U 1975,2039,2103,2167,2231,2295,2359,2423,2487,2551
%N Numbers n such that string 6,7 occurs in the base 8 representation of n but not of n-1.
%H Tanya Khovanova, <a href="http://www.tanyakhovanova.com/RecursiveSequences/NonRecursions.html">Non Recursions</a>
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,8],{6,7}]>0,1,0],{n,2600}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Dec 31 2017 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_