%I A057973
%S A057973 1,2,5,16,55,225,949,4269,19500,91115,429742,2047660,9820197,47383255,
%T A057973 229725560,1118568692,5466616025,26804560282,131817042605,649952289243
%N A057973 Number of polybricks: number of ways to arrange n 1 X 2 "bricks" in a 
               wall (see illustrations).
%C A057973 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 A057973 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 
               (njas(AT)research.att.com)]
%H A057973 Brendan Owen and Livio Zucca, <a href="http://www.geocities.com/liviozuc/
               polymultiforms2.html">Polyform generation</a>
%H A057973 Brendan Owen and Livio Zucca, <a href="a057973a.gif">The 16 polybricks 
               of order 4</a>
%H A057973 N. J. A. Sloane, <a href="a057973.gif">The polybricks of orders 1, 2 
               and 3</a>
%Y A057973 Sequence in context: A066642 A019988 A137732 this_sequence A102461 A052708 
               A149973
%Y A057973 Adjacent sequences: A057970 A057971 A057972 this_sequence A057974 A057975 
               A057976
%K A057973 nonn,nice
%O A057973 1,2
%A A057973 Warren Power (wjpnply(AT)hotmail.com), Oct 21 2000
%E A057973 More terms from Don Reble (djr(AT)nk.ca), Nov 01 2001
%E A057973 Corrected and extended by Joseph Myers (jsm(AT)polyomino.org.uk), Sep 
               21 2002