A123776 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 3 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position.

5, 28, 185, 1287, 9456, 71167, 549076, 4300975, 34154107, 273998400, 2217436152, 18074303774, 148232462372

Offset

1,1

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..13.

Crossrefs

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

Sequence in context: A179326 A156629 A331797 * A070779 A189487 A367049

Adjacent sequences: A123773 A123774 A123775 * A123777 A123778 A123779

Keyword

nonn,hard

Author

Søren Eilers, Oct 29 2006

Status

approved