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 A026209 #9 Jan 31 2020 05:10:56 %S A026209 1,4,2,8,3,12,5,16,6,20,7,24,9,28,10,32,11,36,13,40,14,44,15,48,17,52, %T A026209 18,56,19,60,21,64,22,68,23,72,25,76,26,80,27,84,29,88,30,92,31,96,33, %U A026209 100,34,104,35,108,37,112,38,116,39,120,41 %N A026209 Duplicate of A026185. %K A026209 dead %O A026209 1,2