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A326301 The number of rectangular free polyominoes with n cells where no 4 cells meet at a point. 1

%I

%S 1,2,3,8,19,54,159,511,1676,5685,19512

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

%C 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.

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

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

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

%e L

%e LL and LL

%e LL LLL

%Y Cf. A056780, A002369.

%K nonn,more

%O 1,2

%A _R. J. Mathar_, Oct 17 2019

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Last modified September 19 18:21 EDT 2020. Contains 337181 sequences. (Running on oeis4.)