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 A273880 #13 Jul 23 2025 15:40:16 %S A273880 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,30,22,31,33, %T A273880 34,35,23,36,37,38,39,40,41,43,44,45,46,32,47,48,49,50,51,53,54,55,42, %U A273880 56,57,58,52,59,24,60,61,63,64,65,66,67,68,69,70,71,73,74,75,76,77,78,79,80,81,25,83,84,85,86,87,88,89,90,91,93,94,95,96,97,98,99,100,101 %N A273880 Pick any pair of "2" digits in the sequence. Those two "2"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 A273880 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 A273880 Eric Angelini, <a href="/A273880/b273880.txt">Table of n, a(n) for n = 1..1011</a> %Y A273880 See A273376 for the equivalent sequence dealing with digit-"1" pairs instead of "2". %K A273880 nonn,base %O A273880 1,3 %A A273880 _Eric Angelini_ and _Jean-Marc Falcoz_, Jun 02 2016