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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.
1
1, 1, 3, 4, 12, 18, 52, 83, 235, 389, 1087, 1851, 5113, 8891, 24357, 43045, 117127, 209731, 567487, 1027245, 2766404, 5053521, 13554315, 24954627, 66696366, 123628610, 329400200, 614216837, 1632039074, 3059240151, 8108703876
OFFSET
1,3
LINKS
M. Abrahamsen and S. Eilers, On the asymptotic enumeration of LEGO structures, Exper Math. 20 (2) (2011) 145-152.
B. Durhuus and S. Eilers, On the entropy of LEGO, arXiv:math.CO/0504039
S. Eilers, The LEGO counting problem, Amer. Math. Monthly, 123 (May 2016), 415-426.
CROSSREFS
Sequence in context: A306176 A026744 A347257 * A124817 A306005 A124818
KEYWORD
nonn,more
AUTHOR
Søren Eilers, Oct 29 2006
EXTENSIONS
More terms by Søren Eilers, Sep 12 2018
STATUS
approved