A123837 Number of ways to build a contiguous building with n LEGO blocks of size 3 X 3 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, 4, 7, 10, 13, 61, 154, 256

Offset

1,4

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..10.

Crossrefs

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

Sequence in context: A318774 A341282 A065810 * A125620 A310687 A310688

Adjacent sequences: A123834 A123835 A123836 * A123838 A123839 A123840

Keyword

nonn

Author

Søren Eilers, Oct 29 2006

Status

approved