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.

1, 1, 9, 22, 317, 980, 13801, 48756, 660997, 2505447

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