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 A166874 #3 May 01 2013 21:13:45 %S A166874 1,2,3,5,10,19,20,30,1000,2000,3000 %N A166874 Numbers with vertical symmetry when expressed as Roman numerals. %K A166874 nonn %O A166874 1,2 %A A166874 _Claudio Meller_, Oct 22 2009 %E A166874 Edited by _N. J. A. Sloane_, Oct 25 2009