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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. 0
1, 1, 1, 4, 7, 10, 13, 61, 154, 256 (list; graph; refs; listen; history; text; internal format)
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: A143454 A318774 A065810 * A125620 A310687 A310688

Adjacent sequences:  A123834 A123835 A123836 * A123838 A123839 A123840

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified July 22 20:45 EDT 2019. Contains 325226 sequences. (Running on oeis4.)