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A123764 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.

%I A123764 #42 Dec 06 2023 14:28:10
%S A123764 1,2,7,24,99,416,1854,8407,38970,182742,866442,4140607,19925401,
%T A123764 96430625,469005432,2290860538,11232074043,55255074216,272634835875,
%U A123764 1348823736479,6689314884962,33247860759418,165583649067958,826170069700588,4129098732200830
%N A123764 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.
%C A123764 From _Søren Eilers_, Sep 12 2018: (Start)
%C A123764 The exponential growth is estimated to be 5.203 in Mølck Nilsson's MSc thesis. This puts an end to the speculation that it may be 5 at the end of the paper "Combinatorial aspects of pyramids of one-dimensional pieces of fixed integer length" by Durhuus and Eilers.
%C A123764 a(20)-a(25) follow from Rasmus Mølck Nilsson's extension of A319156 by transfer-matrix methods. (End)
%H A123764 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 A123764 B. Durhuus and S. Eilers, <a href="https://hal.archives-ouvertes.fr/hal-01185593/">Combinatorial aspects of pyramids of one-dimensional pieces of fixed integer length</a>. Drmota, Michael and Gittenberger, Bernhard. 21st International Meeting on Probabilistic, Combinatorial, and Asymptotic Methods in the Analysis of Algorithms (AofA'10), 2010, Vienna, Austria. Discrete Mathematics and Theoretical Computer Science, DMTCS Proceedings vol. AM, 21st International Meeting on Probabilistic, Combinatorial, and Asymptotic Methods in the Analysis of Algorithms (AofA'10), pp.143-158, 2010, DMTCS Proceedings.
%H A123764 B. Durhuus and S. Eilers, <a href="https://arxiv.org/abs/math/0504039">On the entropy of LEGO</a>, arXiv:math/0504039 [math.CO], 2005; Journal of Applied Mathematics & Computing 45 (2014) 433-448.
%H A123764 S. Eilers, <a href="http://www.math.ku.dk/~eilers/lego.html">A LEGO Counting problem</a>, 2005.
%H A123764 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 A123764 R. Mølck Nilsson, <a href="https://www.math.ku.dk/english/research/tfa/ncg/paststudents/ms-theses/RMS_msthesis.pdf">On the number of flat LEGO structures</a> [dead link]. MSc Thesis in mathematics, University of Copenhagen, 2016.
%H A123764 <a href="/wiki/Index_to_OEIS:_Section_Lc#LEGO">Index entry for sequences related to LEGO blocks</a>
%F A123764 a(n) = (A319156(n)+A123765(n))/2. - _Søren Eilers_, Sep 12 2018
%Y A123764 Cf. A123765, A319156.
%K A123764 nonn,hard,more
%O A123764 1,2
%A A123764 _Søren Eilers_, Oct 29 2006
%E A123764 a(20)-a(25) from _Søren Eilers_, Sep 12 2018