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 A086044 #16 Feb 16 2025 08:32:50
%S A086044 1,2,3,4,5,6,7,8,9,10,11,13,2,17,19,21,23,25,27,29,31,16,35,3,39,41,
%T A086044 43,45,47,49,51,18,38,57,4,61,63,65,67,69,71,20,40,60,79,5,83,85,87,
%U A086044 89,91,22,42,62,82,101,6,105,107,109,111,24,44,64,84,104,123,7,127
%N A086044 Position of first occurrence of n in concatenated numbers (A033307, Champernowne constant).
%C A086044 A033307(a(n)) = A000030(n).
%H A086044 Paul Tek, <a href="/A086044/b086044.txt">Table of n, a(n) for n = 0..10000</a>
%H A086044 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ChampernowneConstant.html">Champernowne Constant</a>
%t A086044 With[{ch=Flatten[IntegerDigits/@Range[0,500]]},Table[ SequencePosition[ ch,IntegerDigits[n],1][[1]],{n,0,70}]][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 07 2020 *)
%Y A086044 Cf. A086045, A086048.
%K A086044 nonn,base
%O A086044 0,2
%A A086044 _Reinhard Zumkeller_, Jul 07 2003