%I M3565 #31 Dec 06 2023 01:58:09
%S 1,4,20,110,638,3832,23592,147941,940982,6053180,39299408,257105146,
%T 1692931066,11208974860,74570549714,498174818986,3340366308393
%N Number of fixed n-celled polyominoes which need only touch at corners.
%C Also known as fixed polyplets. - _David Bevan_, Jul 28 2009
%D D. H. Redelmeier, personal communication.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H M. F. Hasler, <a href="/A006770/a006770.png">Illustration of the A006770(3)=20 fixed 3-polyplets</a>, Sep 29 2014.
%H S. Mertens, <a href="http://dx.doi.org/10.1007/BF01026565">Lattice animals: a fast enumeration algorithm and new perimeter polynomials</a>, J. Stat. Phys. 58 (5-6) (1990) 1095-1108, Table 1.
%H H. Redelmeier, <a href="/A006770/a006770.pdf">Emails to N. J. A. Sloane, 1991</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Polyplet.html">Polyplet.</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Pseudo-polyomino">Pseudo polyomino</a>
%e 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
%e 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
%Y Cf. A030222 (free polyplets).
%Y 10th row of A366767.
%K nonn,hard,more
%O 1,2
%A _N. J. A. Sloane_.
%E One more term from _Joseph Myers_, Sep 26 2002
|