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 A236576 #42 Jun 10 2022 06:14:28
%S A236576 1,4,22,121,664,3643,19987,109657,601624,3300760,18109345,99355414,
%T A236576 545105209,2990674357,16408085929,90021597712,493896002842,
%U A236576 2709719309845,14866649448256,81564634762843,447497579542135
%N A236576 The number of tilings of a 5 X (3n) floor with 1 X 3 trominoes.
%C A236576 Tilings are counted irrespective of internal symmetry: Tilings that match each other after rotations and/or reflections are counted with their multiplicity.
%H A236576 G. C. Greubel, <a href="/A236576/b236576.txt">Table of n, a(n) for n = 0..1000</a>
%H A236576 Mudit Aggarwal and Samrith Ram, <a href="https://arxiv.org/abs/2206.04437">Generating functions for straight polyomino tilings of narrow rectangles</a>, arXiv:2206.04437 [math.CO], 2022.
%H A236576 R. J. Mathar, <a href="http://arxiv.org/abs/1311.6135">Paving Rectangular Regions with Rectangular Tiles: Tatami and Non-Tatami Tilings</a>, arXiv:1311.6135 [math.CO], 2013, Table 20.
%H A236576 R. J. Mathar, <a href="http://arxiv.org/abs/1406.7788">Tilings of Rectangular Regions by Rectangular Tiles: Counts Derived from Transfer Matrices</a>, arXiv:1406.7788 [math.CO], 2014.
%H A236576 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (6,-3,1).
%F A236576 G.f.: (1-x)^2/(1-6*x+3*x^2-x^3).
%F A236576 a(n) = 6*a(n-1) - 3*a(n-2) + a(n-3). - _M. Poyraz Torcuk_, Oct 24 2021
%p A236576 g := (1-x)^2/(1-6*x+3*x^2-x^3) ;
%p A236576 taylor(%,x=0,30) ;
%p A236576 gfun[seriestolist](%) ;
%t A236576 CoefficientList[Series[(1 - x)^2/(1 - 6 x + 3 x^2 - x^3), {x,0,50}], x] (* _G. C. Greubel_, Apr 29 2017 *)
%t A236576 LinearRecurrence[{6, -3, 1}, {1, 4, 22}, 30] (* _M. Poyraz Torcuk_, Nov 06 2021 *)
%o A236576 (PARI) my(x='x+O('x^50)); Vec((1-x)^2/(1-6*x+3*x^2-x^3)) \\ _G. C. Greubel_, Apr 29 2017
%Y A236576 Cf. A000930 (3 X n floor), A049086 (4 X 3n floor), A236577, A236578.
%K A236576 nonn,easy
%O A236576 0,2
%A A236576 _R. J. Mathar_, Jan 29 2014