A123772 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.

1, 3, 17, 107, 761, 5607, 42730, 331851, 2618024, 20895964, 168398683, 1367838390, 11184711448, 91976811135

Offset

1,2

Links

Table of n, a(n) for n=1..14.

Crossrefs

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

Sequence in context: A074563 A077145 A299039 * A212524 A103730 A074556

Adjacent sequences: A123769 A123770 A123771 * A123773 A123774 A123775

Keyword

nonn,hard

Author

Søren Eilers, Oct 29 2006

Status

approved