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 A027210 #13 Oct 25 2019 16:51:16
%S A027210 1,9,57,298,1545,7126,34603,151633,714481,3049328,14131926,59385159,
%T A027210 272409611,1133433579,5163641033,21341122875,96751092786,397978832144,
%U A027210 1797722306693,7369285976135,33195299823112,135723491400062,610027809595308,2489247495517382,11168400384253936
%N A027210 a(n) = Sum_{k=0..n-3} T(n,k) * T(n,k+3), with T given by A026725.
%p A027210 A027210 := proc(n)
%p A027210 add( A026725(n,k)*A026725(n,k+3),k=0..n-3) ;
%p A027210 end proc: # _R. J. Mathar_, Oct 21 2019
%K A027210 nonn
%O A027210 3,2
%A A027210 _Clark Kimberling_
%E A027210 Name corrected by _R. J. Mathar_, Oct 21 2019
%E A027210 More terms from _Sean A. Irvine_, Oct 24 2019