A123815 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 8 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.

1, 37, 73, 2995, 9235, 404559, 1360441

Offset

1,2

Comments

The base block is not counted among the n and must be the only block in the bottom layer of the building.

Links

Table of n, a(n) for n=1..7.

Crossrefs

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

Sequence in context: A146241 A217386 A083990 * A289732 A087531 A283718

Adjacent sequences: A123812 A123813 A123814 * A123816 A123817 A123818

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Status

approved