A123767 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 2 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.

1, 4, 7, 28, 67, 289, 723, 3185, 8677, 38580, 109143, 489496, 1430283

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..13.

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

Index entry for sequences related to LEGO blocks

Crossrefs

Sequence in context: A149074 A149075 A149076 * A149077 A149078 A149079

Adjacent sequences: A123764 A123765 A123766 * A123768 A123769 A123770

Keyword

nonn

Author

Søren Eilers, Oct 29 2006

Status

approved