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A001168 Number of fixed polyominoes with n cells.
(Formerly M1639 N0641)
1, 2, 6, 19, 63, 216, 760, 2725, 9910, 36446, 135268, 505861, 1903890, 7204874, 27394666, 104592937, 400795844, 1540820542, 5940738676, 22964779660, 88983512783, 345532572678, 1344372335524, 5239988770268, 20457802016011, 79992676367108, 313224032098244, 1228088671826973 (list; graph; refs; listen; history; text; internal format)



Number of rookwise connected patterns of n square cells.

N. Madras proved in 1999 the existence of lim_{n->oo} a(n+1)/a(n), which is the real limit growth rate of the number of polyominoes; and hence, this limit is equal to lim_{n->oo} a(n)^{1/n}, the well-known Klarner's constant. The currently best-known lower and upper bounds on this constant are 3.9801 (Barequet et al., 2006) and 4.6496 (Klarner and Rivest, 1973), respectively. But see also Knuth (2014).


G Barequet, R Barequet, An Improved Upper Bound on the Growth Constant of Polyominoes, Electronic Notes in Discrete Math., 2015.

G. Barequet, M. Moffie, A. Ribo, and G. Rote, Counting polyominoes on twisted cylinders, Integers (electronic journal, 6 (2006), A22, 37 pp.

Gill Barequet, M Shalah, Improved Bounds on the Growth Constant of Polyiamonds, 32nd European Workshop on Computational Geometry, 2016; http://www.eurocg2016.usi.ch/sites/default/files/paper_19.pdf

Stirling Chow and Frank Ruskey, Gray codes for column-convex polyominoes and a new class of distributive lattices, Discrete Mathematics, 309 (2009), 5284-5297.

A. R. Conway and A. J. Guttmann, On two-dimensional percolation, J. Phys. A: Math. Gen. 28(1995) 891-904.

S. R. Finch, Mathematical Constants, Cambridge, 2003, pp. 378-382.

J. Fortier, A. Goupil, J. Lortie and J. Tremblay, Exhaustive generation of gominoes, Theoretical Computer Science, 2012; http://dx.doi.org/10.1016/j.tcs.2012.02.032. - From N. J. A. Sloane, Sep 20 2012

J. E. Goodman and J. O'Rourke, editors, Handbook of Discrete and Computational Geometry, CRC Press, 1997, p. 229.

A. J. Guttmann, ed., Polygons, Polyominoes and Polycubes, Springer, 2009, p. 478. (Table 16.10 has 56 terms of this sequence.)

I. Jensen and A. J. Guttmann, Statistics of lattice animals (polyominoes) and polygons. J. Phys. A 33, L257-L263 (2000).

D. A. Klarner and R. L. Rivest, A procedure for improving the upper bound for the number of n-ominoes, Canadian J. of Mathematics, 25 (1973), 585-602.

C. Lesieur, L. Vuillon, From Tilings to Fibers - Bio-mathematical Aspects of Fold Plasticity, Chapter 13 (pages 395-422) of "Oligomerization of Chemical and Biological Compounds" (?), 2014; http://dx.doi.org/10.5772/58577

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.

W. F. Lunnon, Counting hexagonal and triangular polyominoes, pp. 87-100 of R. C. Read, editor, Graph Theory and Computing. Academic Press, NY, 1972.

N. Madras, A pattern theorem for lattice clusters, Annals of Combinatorics, 3 (1999), 357-384.

D. H. Redelmeier, Counting polyominoes: yet another attack, Discrete Math., 36 (1981), 191-203.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

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


I. Jensen, Table of n, a(n) for n = 1..56

S. R. Finch, Klarner's Lattice Animal Constant

I. Jensen, Enumerations of lattice animals and trees, arXiv:cond-mat/0007239.

I. Jensen, Home page

I. Jensen, More terms

D. E. Knuth, Program

D. E. Knuth, First 47 terms

D. E. Knuth, Problems That Philippe Would Have Loved, Paris 2014.

Tomás Oliveira e Silva, Enumeration of polyominoes

Jaime Rangel-Mondragón, Polyominoes and Related Families, The Mathematica Journal, Volume 9, Issue 3.

Eric Weisstein's World of Mathematics, Polyomino


For asymptotics, see Knuth (2014).


See Jaime Rangel-Mondragón's article.


Cf. A000105, A006746, A056877, A006748, A056878, A006747, A006749, A006884, A006885, A006877, A006878, A033492.

A006762 is another version.

Sequence in context: A057409 A141771 A001170 * A193111 A119255 A071969

Adjacent sequences:  A001165 A001166 A001167 * A001169 A001170 A001171




N. J. A. Sloane


Extended to n=28 by Tomás Oliveira e Silva

Extended to n=46 by Iwan Jensen

Verified (and one more term found) by Don Knuth, Jan 09 2001

Richard Schroeppel communicated Jensen's calculation of the first 56 terms, Feb 21 2005

Gill Barequet commented on Madras's proof from 1999 of the limit growth rate of this sequence, and provided references to the currently best-known bounds on it, May 24 2011

Incorrect Mathematica program removed by Jean-François Alcover, Mar 24 2015



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Last modified March 26 00:51 EDT 2017. Contains 284111 sequences.