

A366443


Number of free polyominoes of siteperimeter n.


2



0, 0, 0, 1, 0, 1, 1, 5, 5, 23, 46, 187, 552, 2145, 7796
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OFFSET

1,8


COMMENTS

This sequence counts free connected (via common edges) polyominoes with given siteperimeter. The siteperimeter of a polyomino is the number of cells that are adjacent to it (via common edges). This sequence allows holes of any kind.


LINKS



EXAMPLE

a(4) = a(6) = a(7) = 1 as the monomino, domino and Lshaped tromino are the only polyominoes with site perimeter 4, 6 and 7 respectively.
a(5) = 0 as no polyomino has a siteperimeter of 5.
a(8) = 5 as the straight tromino, square tetromino, Ttetromino, Stetromino and cross pentomino are the only polyominoes with site perimeter 8. See link "Examples".


CROSSREFS

Cf. A000105 (free polyominoes), A001971 (the maximum size of a polyomino with siteperimeter n is given by A001971(n2)), A057730 (perimeter instead of siteperimeter), A216820 (fixed version of current sequence).


KEYWORD

nonn,hard,more


AUTHOR



STATUS

approved



