A123827 Number of ways to build a contiguous building with n LEGO blocks of size 2 X 3 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees.

1, 13, 25, 352, 1006, 15510, 46928, 744211, 2479362

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..9.

Index entry for sequences related to LEGO blocks

Crossrefs

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

Sequence in context: A053404 A295794 A122003 * A105796 A226051 A238338

Adjacent sequences: A123824 A123825 A123826 * A123828 A123829 A123830

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Status

approved