A123799 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 6 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.

1, 22, 43, 1039, 3136, 81773, 267670, 7192059

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..8.

Crossrefs

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

Sequence in context: A019508 A166058 A305609 * A138842 A040462 A269310

Adjacent sequences: A123796 A123797 A123798 * A123800 A123801 A123802

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Status

approved