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 A047121 #5 Mar 30 2012 18:56:53
%S A047121 1,2,3,5,9,18,36,69,134,263,526,1052,2085,4143,8250,16500,33000,65851,
%T A047121 131484,262668,525336,1050672,2100045,4198157,8393603,16787206,
%U A047121 33574412,67136750,134255332,268484858,536969716,1073939432,2147761687
%N A047121 Sum{T(i,n-i): i=0,1,...,n}, array T as in A047120.
%K A047121 nonn
%O A047121 0,2
%A A047121 _Clark Kimberling_