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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. 0
1, 1, 1, 2, 3, 4, 5, 11, 22, 34, 47, 113 (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..12.

CROSSREFS

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

Sequence in context: A006481 A118597 A083160 * A274837 A064959 A217650

Adjacent sequences:  A123820 A123821 A123822 * A123824 A123825 A123826

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified June 16 04:56 EDT 2021. Contains 345056 sequences. (Running on oeis4.)