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 A121510 #1 Sep 29 2006 03:00:00 %S A121510 1,2,3,5,18 %N A121510 Conjectured to be complete list of cycle lengths for 3x+1 (or Collatz) problem. %K A121510 nonn %O A121510 1,2 %A A121510 Daniel Asimov (dasimov(AT)earthlink.net), Sep 17 2006