A326301 The number of rectangular free polyominoes with n cells where no 4 cells meet at a point.

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 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 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

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