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 A247740 #6 Feb 06 2017 19:04:29
%S A247740 0,0,0,6,66,772,6760,60122,552930,4887052,42365416,361418592,
%T A247740 3063883318,25819450218,215875963118,1793852851690,14833014554258,
%U A247740 122147248758898,1002084660185318,8192705916505028,66777880125812344,542833111487459532,4401913323626254612,35616479684643020150
%N A247740 Total number of T shapes in all tilings of a 5 X n rectangle with pentominoes of any shape.
%H A247740 Alois P. Heinz, <a href="/A247740/b247740.txt">Table of n, a(n) for n = 0..500</a>
%H A247740 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a>
%F A247740 a(n) = Sum_{k>0} k * A247707(n,k).
%Y A247740 Cf. A174249, A233427, A247707.
%K A247740 nonn
%O A247740 0,4
%A A247740 _Alois P. Heinz_, Sep 23 2014