

A006770


Number of fixed ncelled polyominoes which need only touch at corners.
(Formerly M3565)


4



1, 4, 20, 110, 638, 3832, 23592, 147941, 940982, 6053180, 39299408, 257105146, 1692931066, 11208974860, 74570549714, 498174818986, 3340366308393
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OFFSET

1,2


COMMENTS

Also known as fixed polyplets [From David Bevan, Jul 28 2009]


REFERENCES

D. H. Redelmeier, personal communication.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=1..17.
Eric Weisstein's World of Mathematics, Polyplet.


EXAMPLE

a(2)=4: the two fixed dominoes and the two rotations of the polyplet consisting of two cells touching at a vertex [From David Bevan, Jul 28 2009]


CROSSREFS

Cf. A030222 (free polyplets) [From David Bevan, Jul 28 2009]
Sequence in context: A026127 A222205 A153295 * A158827 A026156 A025183
Adjacent sequences: A006767 A006768 A006769 * A006771 A006772 A006773


KEYWORD

nonn,hard


AUTHOR

N. J. A. Sloane.


EXTENSIONS

One more term from Joseph Myers, Sep 26 2002


STATUS

approved



