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A123833 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 3 X 3 which is symmetric after a rotation by 180 degrees. 0
1, 1, 9, 22, 317, 980, 13801, 48756, 660997, 2505447 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..10.

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: A264651 A113519 A300462 * A084023 A156342 A133769

Adjacent sequences:  A123830 A123831 A123832 * A123834 A123835 A123836

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified April 21 08:03 EDT 2021. Contains 343146 sequences. (Running on oeis4.)