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%I #8 Oct 09 2013 14:20:53
%S 1,1,9,22,317,980,13801,48756,660997,2505447
%N Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 3 X 3 which is symmetric after a rotation by 180 degrees.
%H M. Abrahamsen and S. Eilers, <a href="http://dx.doi.org/10.1080/10586458.2011.564539">On the asymptotic enumeration of LEGO structures</a>, Exper Math. 20 (2) (2011) 145-152.
%H B. Durhuus and S. Eilers, <a href="http://arxiv.org/abs/math/0504039">On the entropy of LEGO</a>, arXiv:math.CO/0504039
%K nonn
%O 1,3
%A _Søren Eilers_, Oct 29 2006
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