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 A072008 #2 Mar 30 2012 18:57:04 %S A072008 2,4,5,8,9,10,11,14,15,17,18,19,20,23,24,25,27,29,31,32,33,35,36,38, %T A072008 39,41,42,43,46,47,48,50,52,54,55,56,59,60,62,63,64,65,66,69,70,72,73, %U A072008 74,77,78,79,81,83,84,86,87,88,91,92,93,95 %N A072008 a(n)=b(3n+1), where b=A072007. %Y A072008 Cf. A072007. %K A072008 nonn %O A072008 1,1 %A A072008 _Clark Kimberling_, Jun 07 2002