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 A247737 #6 Feb 07 2017 10:14:28
%S A247737 0,0,4,24,436,3888,29880,264460,2353136,20400352,171215320,1430108512,
%T A247737 11962161392,99523393628,822501750184,6763177931936,55433124540308,
%U A247737 453013557727460,3690931980743340,29988435689294280,243064471330287696,1965884816120576180
%N A247737 Total number of L shapes in all tilings of a 5 X n rectangle with pentominoes of any shape.
%H A247737 Alois P. Heinz, <a href="/A247737/b247737.txt">Table of n, a(n) for n = 0..500</a>
%H A247737 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a>
%F A247737 a(n) = Sum_{k>0} k * A247704(n,k).
%Y A247737 Cf. A174249, A233427, A247704.
%K A247737 nonn
%O A247737 0,3
%A A247737 _Alois P. Heinz_, Sep 23 2014