

A030222


Number of npolyplets (polyominoes connected at edges or corners); may contain holes.


20



1, 2, 5, 22, 94, 524, 3031, 18770, 118133, 758381, 4915652, 32149296, 211637205, 1401194463, 9321454604, 62272330564, 417546684096
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OFFSET

1,2


COMMENTS

See A056840 for illustrations, valid also for this sequence up to n=4, but slightly misleading for polyplets with holes. See the colored areas in the illustration of A056840(5)=99 which correspond to identical 5polyplets. (The 2+2+43 = 5 additional figures counted there correspond to the 4square configuration with a hole inside ({2,4,6,8} on a numeric keyboard), with one additional square added in three inequivalent places: "inside" one angle (touching two sides), attached to one side, and attached to a corner. These do only count for 3 here, but for 8 in A056840.) It can be seen that A056840 counts a sort of "spanning trees" instead, i.e., simply connected graphs that connect all of the vertices (using only "King's moves", and maybe other additional constraints).  M. F. Hasler, Sep 29 2014


LINKS

Eric Weisstein's World of Mathematics, Polyplet.


EXAMPLE

XXX..XX...XX..X.X..X.. (the 5 for n=3)
.......X...X...X....X.
.....................X


CROSSREFS



KEYWORD

nonn,hard,nice,more


AUTHOR



EXTENSIONS



STATUS

approved



