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A326301 The number of rectangular free polyominoes with n cells where no 4 cells meet at a point. 1
1, 2, 3, 8, 19, 54, 159, 511, 1676, 5685, 19512 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Obtained from the polyominoes of A056780 by discarding the polyominoes that contain 2x2 sub-blocks of 4 cells. One may call this the Tatami version of the free rectangular polyominoes.

This might also be considered a well-defined (or corrected?) version of A002369.

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

from the A056780(4) = 9 polyominoes the one with the 2x2 bounding box is not counted, giving a(4)=8.

From the A056780(5)=21 polyominoes 2 are not counted:

L

LL      and     LL

LL              LLL

CROSSREFS

Cf. A056780, A002369.

Sequence in context: A041281 A078343 A148038 * A148039 A148040 A148041

Adjacent sequences:  A326298 A326299 A326300 * A326302 A326303 A326304

KEYWORD

nonn,more

AUTHOR

R. J. Mathar, Oct 17 2019

STATUS

approved

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Last modified August 14 04:13 EDT 2020. Contains 336477 sequences. (Running on oeis4.)