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 A018221 #13 Aug 03 2017 01:52:53 %S A018221 1,0,6,8,10,12,2,7,3,11,4,9,5,16,24,23,13,26,29,34,32,35,40,15,14,38, %T A018221 17,47,44,18,53,48,20,52,19,21,57,65,25,61,22,66,69,67,28,71,78,27,31, %U A018221 79,84,82,33,30,83,90,89,36,99,95,97,39,100,103,107,37,41,43,110,42 %N A018221 Row 2 of A018219, i.e., (2,n,a_n) is a winning position. %C A018221 Self-inverse when considered as a permutation or function, i.e., a(a(n)) = n. %H A018221 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %K A018221 nonn %O A018221 0,3 %A A018221 _Michael Kleber_ %E A018221 Edited and extended by _Christian G. Bower_, Oct 29 2002