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Numbers k such that 6 and 7 occur juxtaposed in the base-9 representation of k but not of k-1.
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%I #11 Aug 23 2021 10:23:42

%S 61,69,142,150,223,231,304,312,385,393,466,474,547,549,621,636,709,

%T 717,790,798,871,879,952,960,1033,1041,1114,1122,1195,1203,1276,1278,

%U 1350,1365,1438,1446,1519,1527,1600,1608,1681,1689

%N Numbers k such that 6 and 7 occur juxtaposed in the base-9 representation of k but not of k-1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,9],{6,7}]>0 || SequenceCount[IntegerDigits[n,9],{7,6}]>0,1,0],{n,1700}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, May 27 2020 *)

%Y Cf. A007095.

%K nonn,base

%O 1,1

%A _Clark Kimberling_