%I A123771
%S A123771 1,2,12,45,264,1128,6991,32202,202856,973242,6204349
%N A123771 Number of ways, counted up to symmetry, to build a contiguous building 
               with n LEGO blocks of size 1x3 which is symmetric after a rotation 
               by 180 degrees.
%D A123771 M. Abrahamsen and S. Eilers, Efficient counting of LEGO buildings, in 
               preparation
%D A123771 B. Durhuus and S. Eilers, On the entropy of LEGO, arXiv:math.CO/0504039
%H A123771 S. Eilers, <a href="http://www.math.ku.dk/~eilers/lcounts.html">LEGO 
               counts</a>
%Y A123771 Sequence in context: A028570 A009074 A066258 this_sequence A046991 A061990 
               A006742
%Y A123771 Adjacent sequences: A123768 A123769 A123770 this_sequence A123772 A123773 
               A123774
%K A123771 nonn
%O A123771 1,2
%A A123771 Soren Eilers (eilers(AT)math.ku.dk), Oct 29 2006