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%I A123765 #21 Sep 12 2018 06:15:16
%S A123765 1,1,3,4,12,18,52,83,235,389,1087,1851,5113,8891,24357,43045,117127,
%T A123765 209731,567487,1027245,2766404,5053521,13554315,24954627,66696366,
%U A123765 123628610,329400200,614216837,1632039074,3059240151,8108703876
%N A123765 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 2 which is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.
%H A123765 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 A123765 B. Durhuus and S. Eilers, <a href="http://arxiv.org/abs/math/0504039">On the entropy of LEGO</a>, arXiv:math.CO/0504039
%H A123765 S. Eilers, <a href="http://www.jstor.org/stable/10.4169/amer.math.monthly.123.5.415">The LEGO counting problem</a>, Amer. Math. Monthly, 123 (May 2016), 415-426.
%H A123765 <a href="/wiki/Index_to_OEIS:_Section_Lc#LEGO">Index entry for sequences related to LEGO blocks</a>
%K A123765 nonn,more
%O A123765 1,3
%A A123765 _Søren Eilers_, Oct 29 2006
%E A123765 More terms by _Søren Eilers_, Sep 12 2018

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