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 A247741 #6 Feb 06 2017 19:02:54
%S A247741 0,0,0,18,144,1196,10122,92280,821038,6991890,58992846,496243152,
%T A247741 4159529298,34612046520,286233965312,2357133355050,19343135795244,
%U A247741 158206906810656,1289891352293998,10487551431195780,85061169561727062,688372469609962898,5559403964257012514
%N A247741 Total number of U shapes in all tilings of a 5 X n rectangle with pentominoes of any shape.
%H A247741 Alois P. Heinz, <a href="/A247741/b247741.txt">Table of n, a(n) for n = 0..500</a>
%H A247741 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a>
%F A247741 a(n) = Sum_{k>0} k * A247708(n,k).
%Y A247741 Cf. A174249, A233427, A247708.
%K A247741 nonn
%O A247741 0,4
%A A247741 _Alois P. Heinz_, Sep 23 2014