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A123827 Number of ways to build a contiguous building with n LEGO blocks of size 2 X 3 on top of a fixed block of the same size so that the building is symmetric after a rotation by 180 degrees. 64
1, 13, 25, 352, 1006, 15510, 46928, 744211, 2479362 (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..9.

Index entry for sequences related to LEGO blocks

CROSSREFS

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

Sequence in context: A053404 A295794 A122003 * A105796 A226051 A238338

Adjacent sequences:  A123824 A123825 A123826 * A123828 A123829 A123830

KEYWORD

nonn,more

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified October 22 19:53 EDT 2019. Contains 328319 sequences. (Running on oeis4.)