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 A125132 #11 Dec 26 2017 17:31:30 %S A125132 1,3,5,2,7,8,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45, %T A125132 47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91, %U A125132 93,95,97,99,110,10,12,14,16,111,28,30,32,34,36,48,50,52 %N A125132 Self-describing sequence: sequence starts with a(1) = 1 and a(n) is chosen to be the smallest positive number not already in the sequence such that the assertion "sequence gives the positions of the odd digits when the sequence is read as a string of digits" is true. %C A125132 Inspired by Angelini's sequence A114308. %H A125132 Jean-Marc Falcoz, <a href="/A125132/b125132.txt">Table of n, a(n) for n = 1..2001</a> %e A125132 Here are the digits strung together (the odd digits occur at positions that are indexed by terms of the sequence): %e A125132 -135278911 %e A125132 1315171921 %e A125132 2325272931 %e A125132 3335373941... %e A125132 Explanation: a(2)=2? No. a(2)=3? Yes, but then the third term has to be odd and 2 has to appear later. a(3)=2? No, a(3) must be odd, so 5. a(4)? Now we can fill in the 2 that has been waiting. And so on. %Y A125132 Cf. A125133 (missing numbers), A114308 (same except need a(n) > a(n-1)). %K A125132 base,easy,nonn %O A125132 1,2 %A A125132 _N. J. A. Sloane_, Jan 12 2007 %E A125132 Corrected and extended by _D. S. McNeil_, Oct 22 2011