This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A179801 #11 Jul 22 2025 08:23:48
%S A179801 0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,1,1,0,1,
%T A179801 0,0,0,0,0,0,1,1,1,0,1,0,0,0,0,0,1,1,1,1,0,1,0,0,0,0,1,1,1,1,1,0,1,0,
%U A179801 0,0,1,1,1,1,1,1,0,1,0,0,1,1,1,1,1,1,1,0,1,0,1,1,1,1,1,1,1,1,1,0,1
%N A179801 Count of times n appears in number created by stringing together previous n-1 integers.
%C A179801 2 first appears for n=121; 3 first appears for n=1011; 4 first appears for n=1121; 5 first appears for n=10111. - _Harvey P. Dale_, Jul 22 2013
%e A179801 a(6)=0 because stringing together the first 5 integers gives the number "12345" and 6 does not appear in 12345.
%e A179801 a(12)=1 because stringing together the first 11 integers gives "1234567891011" and 12 appears once in 1234567891011 (right at the beginning).
%t A179801 Table[idn=IntegerDigits[n];fid=Flatten[IntegerDigits/@Range[n-1]];Count[ Partition[ fid,Length[idn],1],idn],{n,0,110}] (* _Harvey P. Dale_, Jul 22 2013 *)
%t A179801 Table[SequenceCount[Flatten[IntegerDigits/@Range[n-1]],IntegerDigits[n]],{n,120}] (* _Harvey P. Dale_, Apr 16 2023 *)
%o A179801 (PHP) for($x = 1; $x <= 1000; $x++) {
%o A179801 echo "$x: " . substr_count($running, $x) ."<br />" ;
%o A179801 $running = $running . $x ;
%o A179801 }
%K A179801 nonn,base
%O A179801 1,1
%A A179801 _Dominick Cancilla_, Jul 27 2010