A123823 Number of ways to build a contiguous building with n LEGO blocks of size 2 X 2 on top of a fixed block of the same size so that the building is symmetric after a rotation by 90 degrees.

1, 1, 1, 2, 3, 4, 5, 11, 22, 34, 47, 113

Offset: 1

Author

Søren Eilers, Oct 29 2006

Keywords

• nonn

Comments

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

Crossrefs

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