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A123799 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 6 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees. 0
1, 22, 43, 1039, 3136, 81773, 267670, 7192059 (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..8.

CROSSREFS

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

Sequence in context: A019508 A166058 A305609 * A138842 A040462 A269310

Adjacent sequences:  A123796 A123797 A123798 * A123800 A123801 A123802

KEYWORD

nonn,more

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified August 12 23:52 EDT 2022. Contains 356077 sequences. (Running on oeis4.)