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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
OFFSET
1,2
COMMENTS
Obtained from the polyominoes of A056780 by discarding the polyominoes that contain 2 X 2 subblocks 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.
EXAMPLE
From the A056780(4) = 9 polyominoes the one with the 2 X 2 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
Sequence in context: A041281 A078343 A148038 * A148039 A148040 A148041
KEYWORD
nonn,more
AUTHOR
R. J. Mathar, Oct 17 2019
STATUS
approved