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 A247745 #6 Feb 06 2017 18:58:00
%S A247745 0,0,0,12,224,2096,17732,160624,1498176,13404068,115123856,980282312,
%T A247745 8327179132,70264899456,587727020332,4882463109244,40378339971868,
%U A247745 332612594766452,2729309532474820,22316919930250328,181922495487675520,1479018078159317720
%N A247745 Total number of Y shapes in all tilings of a 5 X n rectangle with pentominoes of any shape.
%H A247745 Alois P. Heinz, <a href="/A247745/b247745.txt">Table of n, a(n) for n = 0..500</a>
%H A247745 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a>
%F A247745 a(n) = Sum_{k>0} k * A247712(n,k).
%Y A247745 Cf. A174249, A233427, A247712.
%K A247745 nonn
%O A247745 0,4
%A A247745 _Alois P. Heinz_, Sep 23 2014