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 A084480 #23 Jan 24 2025 12:16:48
%S A084480 1,2,10,42,182,790,3432,14914,64814,281680,1224182,5320310,23122148,
%T A084480 100489226,436727814,1898026232,8248853134,35849651070,155803171860,
%U A084480 677123141810,2942788286798,12789406189672,55582969192486,241564496305670,1049843265359828
%N A084480 Number of tilings of a 4 X 2n rectangle with L tetrominoes.
%H A084480 Colin Barker, <a href="/A084480/b084480.txt">Table of n, a(n) for n = 0..1000</a>
%H A084480 Nicolas Bělohoubek and Antonín Slavík, <a href="https://msekce.karlin.mff.cuni.cz/~slavik/papers/L-tetromino-tilings.pdf">L-Tetromino Tilings and Two-Color Integer Compositions</a>, Univ. Karlova (Czechia, 2025). See p. 2.
%H A084480 Cristopher Moore, <a href="https://arxiv.org/abs/math/9905012">Some Polyomino Tilings of the Plane</a>, arXiv:9905012 [math.CO], 1999.
%H A084480 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4,2,-1,-4,-4,-2).
%F A084480 G.f.: (1-2*z-z^3) / (1-4*z-2*z^2+z^3+4*z^4+4*z^5+2*z^6).
%F A084480 a(n) = 4*a(n-1) + 2*a(n-2) - a(n-3) - 4*a(n-4) - 4*a(n-5) - 2*a(n-6) for n>5. - _Colin Barker_, Mar 28 2017
%t A084480 LinearRecurrence[{4, 2, -1, -4, -4, -2}, {1, 2, 10, 42, 182, 790}, 25] (* _Jean-François Alcover_, Feb 25 2020 *)
%o A084480 (PARI) Vec((1 - 2*x - x^3) / (1 - 4*x - 2*x^2 + x^3 + 4*x^4 + 4*x^5 + 2*x^6) + O(x^30)) \\ _Colin Barker_, Mar 28 2017
%Y A084480 Cf. A084478, A084479, A084477, A084481, A174248, A226322, A232497.
%K A084480 nonn,easy
%O A084480 0,2
%A A084480 _Ralf Stephan_, May 27 2003
%E A084480 Inserted a(0)=1 by _Alois P. Heinz_, May 01 2013