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A232684 Number of tilings of a 6 X 2n rectangle with 3n tetrominoes of any shape.

%I A232684 #25 Feb 07 2017 16:59:25
%S A232684 1,9,2003,178939,22483347,2569437089,304446920314,35704534261665,
%T A232684 4203065267122878,494232382069456694,58138539945306221167,
%U A232684 6838279451118114249916,804352962762109905924360,94610929453211737452277488,11128526714790919845521179844
%N A232684 Number of tilings of a 6 X 2n rectangle with 3n tetrominoes of any shape.
%H A232684 Alois P. Heinz, <a href="/A232684/b232684.txt">Table of n, a(n) for n = 0..300</a>
%H A232684 S. Butler, J. Ekstrand, S. Osborne, <a href="/A230031/a230031.pdf">TETRIS Tiling</a>, AMS Spring Central Sectional, Iowa State University, April 27-28 2013
%H A232684 Wikipedia, <a href="https://en.wikipedia.org/wiki/Tetromino">Tetromino</a>
%e A232684 a(1) = 9:
%e A232684 .___. .___. .___. .___. .___. .___. .___. .___. .___.
%e A232684 |   | | | | |   | |_. | |   | | ._| |   | | ._| |_. |
%e A232684 |___| | | | |___| | | | |___| | | | |___| | | | | | |
%e A232684 |   | | | | | | | | |_| |_. | |_| | | ._| |_| | | |_|
%e A232684 |___| |_|_| | | | |___| | | | |___| | | | | | | | | |
%e A232684 |   | |   | | | | |   | | |_| |   | |_| | | |_| |_| |
%e A232684 |___| |___| |_|_| |___| |___| |___| |___| |___| |___|.
%Y A232684 Cf. A174248, A232698, A232722.
%Y A232684 Even bisection of column k=6 of A230031.
%K A232684 nonn
%O A232684 0,2
%A A232684 _Alois P. Heinz_, Nov 27 2013