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

1,3

Links

Table of n, a(n) for n=1..22.

Crossrefs

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

Sequence in context: A304988 A108653 A316194 * A290433 A251582 A328773

Adjacent sequences: A123770 A123771 A123772 * A123774 A123775 A123776

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Extensions

More terms by Søren Eilers, Sep 12 2018

Status

approved