A123821 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.

9, 97, 1349, 20288, 329707, 5574248, 97506021, 1747201171, 31923371982, 592403479154

Offset: 1

Author

Søren Eilers, Oct 29 2006

Keywords

• nonn
• hard

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.