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A123821 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. 0
9, 97, 1349, 20288, 329707, 5574248, 97506021, 1747201171, 31923371982, 592403479154 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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..10.

CROSSREFS

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

Sequence in context: A194725 A218500 A293986 * A145509 A098782 A076758

Adjacent sequences:  A123818 A123819 A123820 * A123822 A123823 A123824

KEYWORD

nonn,hard

AUTHOR

Søren Eilers, Oct 29 2006

STATUS

approved

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Last modified November 18 14:59 EST 2019. Contains 329262 sequences. (Running on oeis4.)