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%I #9 Feb 06 2017 14:44:21
%S 1,1,117,178939,19077209438,72713560548906621
%N Number of tilings of an 2n X 2n square using tetrominoes of any shape.
%H 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 R. S. Harris, <a href="http://www.bumblebeagle.org/polyominoes/tilingcounting">Counting Polyomino Tilings</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Tetromino">Tetromino</a>
%F a(n) = A230031(2n,2n).
%Y Bisection (even part) of main diagonal of A230031.
%Y Cf. A004003.
%K nonn,more
%O 0,3
%A _Alois P. Heinz_, Oct 17 2015
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