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 A027290 #8 Oct 26 2019 23:08:59
%S A027290 3,9,73,230,1335,4376,22144,74766,351558,1213965,5458347,19181130,
%T A027290 83735127,298391598,1276135088,4599546922,19380537318,70514368558,
%U A027290 293838981413,1077617352348,4452600188602,16440039884624,67481063581593,250610375841434,1023303550651792
%N A027290 a(n) = Sum_{k=0..floor(n/2)-2} T(n,k) * T(n,k+3), with T given by A026009.
%K A027290 nonn
%O A027290 4,1
%A A027290 _Clark Kimberling_
%E A027290 More terms from _Sean A. Irvine_, Oct 26 2019