A123836 Number of ways to build a contiguous building with n LEGO blocks of size 3 X 3 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.

1, 9, 17, 186, 523, 6478, 19077, 247945, 796692

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..9.

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: A132375 A110360 A371031 * A141444 A061748 A159510

Adjacent sequences: A123833 A123834 A123835 * A123837 A123838 A123839

Keyword

nonn

Author

Søren Eilers, Oct 29 2006

Status

approved