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 A027281 #9 Oct 26 2019 22:49:27
%S A027281 1,6,21,76,235,738,2177,6424,18423,52590,147917,413796,1147523,
%T A027281 3166842,8689305,23745584,64621199,175277574,473909989,1277864060,
%U A027281 3436938267,9223203858,24699503281,66020102472,176160084775,469293598878
%N A027281 a(n) = Sum_{k=0..2n} (k+1) * A026568(n, k).
%F A027281 G.f.: (2x^2+4x+1)/(1-x-4x^2)^2.
%K A027281 nonn
%O A027281 0,2
%A A027281 _Clark Kimberling_