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 A273887 #10 Jun 09 2016 08:36:54 %S A273887 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25, %T A273887 26,27,28,30,29,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48, %U A273887 50,51,52,49,53,54,55,56,57,58,60,61,62,63,64,59,65,66,67,68,70,69,71,72 %N A273887 Pick any pair of "9" digits in the sequence. Those two "9"s are separated by k digits. This is the lexicographically earliest sequence of distinct terms in which all the resulting values of k are distinct. %C A273887 The sequence starts with a(1)=0. It is then always extended with the smallest integer not yet present and not leading to a contradiction (which would mean producing a value of k already seen). %H A273887 Eric Angelini, <a href="/A273887/b273887.txt">Table of n, a(n) for n = 1..1011</a> %Y A273887 See A273376 for the equivalent sequence dealing with digit-"1" pairs instead of "9" %K A273887 nonn,base %O A273887 1,3 %A A273887 _Eric Angelini_ and _Jean-Marc Falcoz_, Jun 02 2016