%I A001168 M1639 N0641
%S A001168 1,2,6,19,63,216,760,2725,9910,36446,135268,505861,1903890,7204874,
%T A001168 27394666,104592937,400795844,1540820542,5940738676,22964779660,
%U A001168 88983512783,345532572678,1344372335524,5239988770268,20457802016011,79992676367108,
               313224032098244,1228088671826973
%N A001168 Number of fixed polyominoes with n cells.
%D A001168 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A001168 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A001168 Stirling Chow and Frank Ruskey, Gray codes for column-convex polyominoes 
               and a new class of distributive lattices, Discrete Mathematics, 309 
               (2009), 5284-5297. [From N. J. A. Sloane, Sep 15 2009]
%D A001168 A. R. Conway and A. J. Guttmann, On two-dimensional percolation, J. Phys. 
               A: Math. Gen. 28(1995) 891-904.
%D A001168 S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 378-382.
%D A001168 J. E. Goodman and J. O'Rourke, editors, Handbook of Discrete and Computational 
               Geometry, CRC Press, 1997, p. 229.
%D A001168 I. Jensen, Enumerations of lattice animals and trees, arXiv:cond-mat/
               0007239.
%D A001168 I. Jensen and A. J. Guttmann, Statistics of lattice animals (polyominoes) 
               and polygons. J. Phys. A 33, L257-L263 (2000).
%D A001168 W. F. Lunnon, Counting polyominoes, pp. 347-372 of A. O. L. Atkin and 
               B. J. Birch, editors, Computers in Number Theory. Academic Press, 
               NY, 1971.
%D A001168 W. F. Lunnon, Counting hexagonal and triangular polyominoes, pp. 87-100 
               of R. C. Read, editor, Graph Theory and Computing. Academic Press, 
               NY, 1972.
%D A001168 D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete 
               Math., 36 (1981), 191-203.
%H A001168 I. Jensen, <a href="b001168.txt">Table of n, a(n) for n = 1..56</a>
%H A001168 S. R. Finch, <a href="http://algo.inria.fr/bsolve/constant/rndprc/anml.html">
               Klarner's Lattice Animal Constant</a>
%H A001168 I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/">Home page</a>
%H A001168 I. Jensen, <a href="http://www.ms.unimelb.edu.au/~iwan/animals/series/
               square.site.ser">More terms</a>
%H A001168 D. E. Knuth, <a href="http://www-cs-faculty.stanford.edu/~knuth/programs.html#polyominoes">
               Program</a>
%H A001168 D. E. Knuth, <a href="a1168.txt">First 47 terms</a>
%H A001168 Tomas Oliveira e Silva, <a href="http://www.ieeta.pt/~tos/animals.html">
               Enumeration of polyominoes</a>
%H A001168 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               Polyomino.html">Polyomino</a>
%Y A001168 Cf. A000105, A006746, A056877, A006748, A056878, A006747, A006749, A006884, 
               A006885, A006877, A006878, A033492.
%Y A001168 A006762 is another version.
%Y A001168 Sequence in context: A057409 A141771 A001170 this_sequence A119255 A071969 
               A063030
%Y A001168 Adjacent sequences: A001165 A001166 A001167 this_sequence A001169 A001170 
               A001171
%K A001168 nonn,nice
%O A001168 1,2
%A A001168 N. J. A. Sloane (njas(AT)research.att.com).
%E A001168 Extended to n=28 by Tomas Oliveira e Silva. Extended to n=46 by Iwan 
               Jensen. Verified (and one more term found) by D. E. Knuth, Jan 09 
               2001.
%E A001168 Richard Schroeppel communicated Jensen's calculation of the first 56 
               terms, Feb 21 2005