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 A099521 #4 Jun 29 2013 06:20:35 %S A099521 1,2,5,3,4,9,6,11,54,8,7,10,19,12,72,21,14,23,84,16,25,13,18,29,15,22, %T A099521 33,17,26,37,156,28,39,30,41,190,32,45,34,47,218,36,51,20,40,57,42,59, %U A099521 27,44,24,46,284,48,286,31,50,292,52,77,300,79,35,81,85,56,87,58,89,60 %N A099521 a(n) is such that A099520(a(n))=n. %e A099521 Gives the positions in the sequence A099520 at which the integers n>0 appear. A099520 begins: 1,2,4,5,3,7,11,10,6,12,8,..., so the positions of the integers are: 1,2,5,3,4,9,6,... %Y A099521 Cf. A099520. Also A099506 and A099507 for sequences based on a slightly different definition. %K A099521 easy,nonn %O A099521 1,2 %A A099521 Mark Hudson (mrmarkhudson(AT)hotmail.com), Oct 20 2004