%I #10 Aug 28 2021 03:05:57
%S 27,72,127,172,227,279,327,372,427,472,527,572,627,672,729,772,827,
%T 872,927,972,1027,1072,1127,1172,1227,1279,1327,1372,1427,1472,1527,
%U 1572,1627,1672,1729,1772,1827,1872,1927,1972,2027
%N Numbers k such that 2 and 7 occur juxtaposed in the base10 representation of k but not of k+1.
%t Transpose[SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{2,7}]>0SequenceCount[IntegerDigits[n],{7,2}]>0,1,0],{n,2100}],{1,0}]][[1]] (* The program uses the SequencePosition and SequenceCount functions from Mathematica version 10 *) (* _Harvey P. Dale_, May 23 2015 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_
