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 A027098 #4 Mar 30 2012 18:56:14 %S A027098 1,2,6,19,55,161,469,1362,3954,11483,33379,97146,283114,826214, %T A027098 2414366,7064217,20693797,60686847,178152055,523473326,1539479414, %U A027098 4531059224,13345835288,39335816471,116012701523,342356498884 %N A027098 T(n,n) + T(n,n+1) + ... + T(n,2n), T given by A027082. %K A027098 nonn %O A027098 0,2 %A A027098 _Clark Kimberling_