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A123822 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 180 degrees. 0
1, 5, 9, 44, 111, 576, 1541, 8199, 23750, 127654, 384817, 2083235 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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: A176967 A110421 A176751 * A226065 A321718 A304127

Adjacent sequences:  A123819 A123820 A123821 * A123823 A123824 A123825

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified May 9 07:57 EDT 2021. Contains 343693 sequences. (Running on oeis4.)