A123765 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 2 which is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.

1, 1, 3, 4, 12, 18, 52, 83, 235, 389, 1087, 1851, 5113, 8891, 24357, 43045, 117127, 209731, 567487, 1027245, 2766404, 5053521, 13554315, 24954627, 66696366, 123628610, 329400200, 614216837, 1632039074, 3059240151, 8108703876

Offset

1,3

Links

Table of n, a(n) for n=1..31.

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

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: A306176 A026744 A347257 * A124817 A306005 A124818

Adjacent sequences: A123762 A123763 A123764 * A123766 A123767 A123768

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Extensions

More terms by Søren Eilers, Sep 12 2018

Status

approved