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 A049721 #4 Mar 30 2012 18:56:56 %S A049721 6,8,9,15,22,30,39,52,64,79,94,112,131,152,173,197,222,251,279,308, %T A049721 339,373,408,445,482,524,563,606,648,695,742,792,843,892,949,1003, %U A049721 1058,1117,1175,1242,1303,1366,1432,1501,1572,1640,1711 %N A049721 a(n)=T(n,2), array T as in A048149. %K A049721 nonn %O A049721 0,1 %A A049721 _Clark Kimberling_