A123801 - OEIS

A123801

Number of ways to build a contiguous building with n LEGO blocks of size 1 X 6 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.

1, 4, 7, 31, 76, 365, 920, 4691, 12695, 65708, 184458, 967195, 2798734, 14837523, 43829052, 234029147, 703643181

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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..17.

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

CROSSREFS

Sequence in context: A080871 A358586 A102666 * A359706 A156228 A218959

Adjacent sequences: A123798 A123799 A123800 * A123802 A123803 A123804

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

EXTENSIONS

a(12)-a(17) from Søren Eilers, Sep 16 2018

STATUS

approved