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 A006770 Number of fixed n-celled polyominoes which need only touch at corners. (Formerly M3565) 5
 1, 4, 20, 110, 638, 3832, 23592, 147941, 940982, 6053180, 39299408, 257105146, 1692931066, 11208974860, 74570549714, 498174818986, 3340366308393 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Also known as fixed polyplets. - 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 M. F. Hasler, Illustration of the A006770(3)=20 fixed 3-polyplets, Sep 29 2014. S. Mertens, Lattice animals: a fast enumeration algorithm and new perimeter polynomials, J. Stat. Phys. 58 (5-6) (1990) 1095-1108, Table 1. 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. - David Bevan, Jul 28 2009 a(3)=20 counts 4 rotations (by 0°, 45°, 90°, 135°) of the straight ... trinomino, and 8 rotations (by multiples of 45°) of the L-shaped .: trinomino and the ..· 3-polyplet, cf. link to the image. - M. F. Hasler, Sep 30 2014 CROSSREFS Cf. A030222 (free polyplets). Sequence in context: A262394 A271932 A153295 * A158827 A263854 A026156 Adjacent sequences:  A006767 A006768 A006769 * A006771 A006772 A006773 KEYWORD nonn,hard,more AUTHOR EXTENSIONS One more term from Joseph Myers, Sep 26 2002 STATUS approved

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