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%I #11 Oct 19 2017 03:13:52
%S 1,2,5,16,55,225,949,4269,19500,91115,429742,2047660,9820197,47383255,
%T 229725560,1118568692,5466616025,26804560282,131817042605,649952289243
%N Number of polybricks: number of ways to arrange n 1 X 2 "bricks" in a wall (see illustrations).
%C The tiling of bricks is topologically the same as that by regular hexagons and this sequence can also be seen as counting polyhexes where two polyhexes are equivalent iff they are related by a symmetry that is also a symmetry of the tiling by bricks.
%D Other references on polyforms are: www.mathpuzzle.com, Solomon W. Golomb, Ed Pegg, Eric Weisstein, David A. Klarner (Packing rectangles) and Michael Reid [These references should be expanded! - _N. J. A. Sloane_]
%H Brendan Owen and Livio Zucca, <a href="http://www.iread.it/lz/polymultiforms2.html">Polyform generation</a>
%H Brendan Owen and Livio Zucca, <a href="/A057973/a057973a.gif">The 16 polybricks of order 4</a>
%H N. J. A. Sloane, <a href="/A057973/a057973.gif">The polybricks of orders 1, 2 and 3</a>
%K nonn,nice
%O 1,2
%A Warren Power (wjpnply(AT)hotmail.com), Oct 21 2000
%E More terms from _Don Reble_, Nov 01 2001
%E Corrected and extended by _Joseph Myers_, Sep 21 2002
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