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A123793 Number of ways to build a contiguous building with n LEGO blocks of size 1 X 5 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees. 0
1, 3, 5, 18, 42, 170, 405, 1769, 4507, 20081, 53008, 240428, 652160, 3002052, 8299727, 38570944, 108387118, 507729121, 1444491686, 6809942459 (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..20.

CROSSREFS

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

Sequence in context: A143546 A069066 A011964 * A196420 A199676 A303684

Adjacent sequences:  A123790 A123791 A123792 * A123794 A123795 A123796

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

EXTENSIONS

a(12)-a(20) from Søren Eilers, Sep 16 2018

STATUS

approved

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Last modified October 17 21:17 EDT 2021. Contains 348065 sequences. (Running on oeis4.)