

A319321


a(n) is the number of d+/d diagonally convex polyplets (polyominoes which need only touch at corners) with n cells.


0



1, 4, 20, 108, 600, 3368, 18968, 106906, 602532, 3395402, 19131460, 107788900, 607274848
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OFFSET

1,2


COMMENTS

A polyplet is d+ [d] diagonally convex if the intersection of its interior with any line of slope 1 [1] through the centers of the cells is connected.


LINKS



EXAMPLE

The only tetraplets that are not d+ diagonally convex are two animals consisting of a horizontal domino and a vertical domino joined at a corner. So a(4) = A006770(4)  2 = 108.


CROSSREFS

Cf. A006770 (fixed polyplets), A187077 (row convex polyplets), A187276 (d+/d diagonally convex polyominoes).


KEYWORD

nonn,more


AUTHOR



STATUS

approved



