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 A018220 #14 Aug 03 2017 01:59:46 %S A018220 2,4,0,3,1,6,5,12,15,17,14,20,7,19,10,8,28,9,31,13,11,32,38,33,41,43, %T A018220 40,42,16,49,51,18,21,23,53,59,61,63,22,66,26,24,27,25,67,75,68,78,76, %U A018220 29,79,30,85,34,88,87,93,95,97,35,100,36,98,37,99,106,39,44,46,111,114 %N A018220 Row 1 of A018219, i.e., (1, n, a_n) is a winning position. %C A018220 Self-inverse when considered as a permutation or function, i.e., a(a(n)) = n. %H A018220 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %K A018220 nonn %O A018220 0,1 %A A018220 _Michael Kleber_ %E A018220 Edited and extended by _Christian G. Bower_, Oct 29 2002