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%I #14 Sep 24 2024 14:41:27
%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 2 X 2 subblocks 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 2 X 2 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