A123773 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 3 which is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.

1, 1, 3, 4, 16, 24, 103, 163, 721, 1173, 5283, 8783, 39912, 67381, 308314, 526553, 2421040, 4172834, 19257309, 33438244, 154761065, 270372085

Offset: 1

Author

Søren Eilers, Oct 29 2006

Keywords

• nonn
• more

Crossrefs

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

Extensions

More terms by Søren Eilers, Sep 12 2018