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A123767
Number of ways to build a contiguous building with n LEGO blocks of size 1 X 2 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.
0
1, 4, 7, 28, 67, 289, 723, 3185, 8677, 38580, 109143, 489496, 1430283
OFFSET
1,2
COMMENTS
The base block is not counted among the n and must be the only block in the bottom layer of the building.
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/0504039 [math.CO], 2005.
S. Eilers, The LEGO counting problem, Amer. Math. Monthly, 123 (May 2016), 415-426.
CROSSREFS
Sequence in context: A149074 A149075 A149076 * A149077 A149078 A149079
KEYWORD
nonn
AUTHOR
Søren Eilers, Oct 29 2006
STATUS
approved