A123843 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 90 degrees.

1, 1, 1, 7, 13, 19, 25, 209, 571

Offset

1,4

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/0504039 [math.CO], 2005.

S. Eilers, A LEGO Counting problem, 2005.

Crossrefs

Sequence in context: A354936 A348932 A184521 * A277093 A004082 A246294

Adjacent sequences: A123840 A123841 A123842 * A123844 A123845 A123846

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Status

approved