A123771 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 3 which is symmetric after a rotation by 180 degrees.

1, 2, 12, 45, 264, 1128, 6991, 32202, 202856, 973242, 6204349

Offset: 1

Author

Søren Eilers, Oct 29 2006

Keywords

• nonn
• more

Links

• S. Eilers, The LEGO counting problem, Amer. Math. Monthly, 123 (May 2016), 415-426.
• Index entry for sequences related to LEGO blocks

Crossrefs

Cf. A112389, A123762-A123827, A123829-A123849.