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A123849 Number of ways to build a contiguous building with n LEGO blocks of size 5 X 5 on top of a fixed block of the same size so that the building is symmetric after a rotation by 90 degrees. 64
1, 1, 1, 11, 21, 31, 41 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

The base block is not counted among the n and must be the only block in the bottom layer of the building.

LINKS

Table of n, a(n) for n=1..7.

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.

B. Durhuus and S. Eilers, On the entropy of LEGO, J. Appl. Math. Comput. 45 (1-2) (2014), 433-448.

S. Eilers, The LEGO counting problem, Amer. Math. Monthly, 123 (May 2016), 415-426.

CROSSREFS

Sequence in context: A049201 A068633 A225297 * A108812 A216100 A017281

Adjacent sequences:  A123846 A123847 A123848 * A123850 A123851 A123852

KEYWORD

nonn,more

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified March 18 16:00 EDT 2019. Contains 321292 sequences. (Running on oeis4.)