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

Author

Søren Eilers, Oct 29 2006

Keywords

• nonn

Links

• 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