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A123842 Number of ways to build a contiguous building with n LEGO blocks of size 4 X 4 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees. 0
1, 21, 41, 903, 2641, 62831, 195929, 4771243 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=1..8.

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, A LEGO Counting problem, 2005.

CROSSREFS

Sequence in context: A195034 A067344 A053428 * A247387 A120772 A260749

Adjacent sequences:  A123839 A123840 A123841 * A123843 A123844 A123845

KEYWORD

nonn,more

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified October 14 00:02 EDT 2019. Contains 327987 sequences. (Running on oeis4.)