A123831 Number of ways to build a contiguous building with n LEGO blocks of size 2 X 4 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.

2, 24, 88, 1079, 5563, 74597, 412309, 5633649

Offset

1,1

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..8.

Crossrefs

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

Sequence in context: A119068 A068379 A136280 * A138648 A172225 A145889

Adjacent sequences: A123828 A123829 A123830 * A123832 A123833 A123834

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Status

approved