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 A018781 #3 Nov 10 2007 03:00:00 %S A018781 1,3,11,31,33,93,341,1023 %N A018781 Duplicate of A003523. %K A018781 dead %O A018781 1,2