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 A050021 #8 Sep 06 2015 18:56:12 %S A050021 1,4,12,20,3,11,15,19,36,2,40,10,44,87,14,48,18,78,35,5,95,39,138,69, %T A050021 9,99,43,86,211,13,30,47,241,159,17,215,77,34,64,21,245,163,94,150,38, %U A050021 288,137,68,124,8,249,98,318,236,42,85,141,495,210 %N A050021 a(n) = position of n in A050020. %H A050021 Ivan Neretin, <a href="/A050021/b050021.txt">Table of n, a(n) for n = 1..1000</a> %K A050021 nonn,easy %O A050021 1,2 %A A050021 _Clark Kimberling_ %E A050021 Three terms corrected by _Ivan Neretin_, Sep 06 2015