

A000170


Number of ways of placing n nonattacking queens on n X n board.
(Formerly M1958 N0775)


46



1, 0, 0, 2, 10, 4, 40, 92, 352, 724, 2680, 14200, 73712, 365596, 2279184, 14772512, 95815104, 666090624, 4968057848, 39029188884, 314666222712, 2691008701644, 24233937684440, 227514171973736, 2207893435808352, 22317699616364044
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OFFSET

1,4


REFERENCES

J. R. Bitner and E. M. Reingold, Backtrack programming techniques, Commun. ACM, 18 (1975), 651656.
J. Freeman, A neural network solution to the nqueens problem, The Mathematica J., 3 (No. 3, 1993), 5256.
M. Gardner, The Unexpected Hanging, pp. 1902, Simon & Shuster NY 1969
Jieh Hsiang, YuhPyng Shieh and YaoChiang Chen, The cyclic complete mappings counting problems, in Problems and Problem Sets for ATP, volume 0210 of DIKU technical reports, G. Sutcliffe, J. Pelletier and C. Suttner, eds., 2002.
Kenji Kise, Takahiro Katagiri, Hiroki Honda and Toshitsugu Yuba: Solving the 24queens Problem using MPI on a PC Cluster, Technical Report UECIS20046, Graduate School of Information Systems, The University of ElectroCommunications (2004)
E. Masehian, H. Akbaripour, N. MohabbatiKalejahi, Landscape analysis and efficient metaheuristics for solving the nqueens problem, Computational Optimization and Applications, 2013; DOI 10.1007/s105890139578z.
M. A. SainteLaguë, Les Réseaux (ou Graphes), Mémorial des Sciences Mathématiques, Fasc. 18, GauthierVillars, Paris, 1926, p. 47.
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).
R. J. Walker, An enumerative technique for a class of combinatorial problems, pp. 9194 of Proc. Sympos. Applied Math., vol. 10, Amer. Math. Soc., 1960.
M. B. Wells, Elements of Combinatorial Computing. Pergamon, Oxford, 1971, p. 238.


LINKS

Table of n, a(n) for n=1..26.
Amazing Mathematical Object Factory, Information on the n Queens problem
D. Bill, Durango Bill's The NQueens Problem
W. Kosters, nQueens bibliography
V. Kotesovec, Nonattacking chess pieces, 6ed
E. Masehian, H. Akbaripour, N. MohabbatiKalejahi, Solving the n Queens Problem using a Tuned Hybrid Imperialist Competitive Algorithm, 2013;
Bernd Nägel, Thomas B. Preußer, Rainer G. Spallek, Queens(AT)TUD project website.
I. Rivin, I. Vardi and P. Zimmermann, The nqueens problem, Amer. Math. Monthly, 101 (1994), 629639.
Eric Weisstein's World of Mathematics, Queens Problem
Cheng Zhang, Jianpeng Ma, Counting Solutions for the Nqueens and Latin Square Problems by Efficient Monte Carlo Simulations, 2008


FORMULA

Strong conjecture : there is a constant c around 2.54 such that a(n) is asymptotic to n!/c^n; weak conjecture : lim n > infinity (1/n) * ln(n!/a(n)) = constant =0.90....  Benoit Cloitre, Nov 10 2002


EXAMPLE

a(2) = a(3) = 0, since on 2 X 2 and 3 X 3 chessboards there are no solutions.


CROSSREFS

See A140393 for another version. Cf. A002562, A065256.
Cf. A036464 (2Q), A047659 (3Q), A061994 (4Q), A108792 (5Q), A176186 (6Q).
Cf. A099152, A006717, A051906.
Sequence in context: A189869 A054790 A140393 * A038216 A213603 A145911
Adjacent sequences: A000167 A000168 A000169 * A000171 A000172 A000173


KEYWORD

nonn,hard,nice


AUTHOR

N. J. A. Sloane.


EXTENSIONS

Terms for n=2123 computed by Sylvain PION (Sylvain.Pion(AT)sophia.inria.fr) and JoelYann FOURRE (JoelYann.Fourre(AT)ens.fr).
a(24) from Kenji KISE (kis(AT)is.uec.ac.jp), Sep 01 2004
a(25) from Objectweb ProActive INRIA Team (proactive(AT)objectweb.org), Jun 11 2005 [Communicated by Alexandre Di Costanzo (Alexandre.Di_Costanzo(AT)sophia.inria.fr)]. This calculation took about 53 years of CPU time.
a(25) has been confirmed by the NTU 25Queen Project at National Taiwan University and Ming Chuan University, led by YuhPyng (Arping) Shieh, Jul 26 2005. This computation took 26613 days CPU time.
Some of the links may be broken. I would appreciate receiving updates to them.  N. J. A. Sloane, May 01 2006
The NQueensatHome web site gives a different value for a(24), 226732487925864. Thanks to Goran Fagerstrom for pointing this out. I do not know which value is correct. I have therefore created a new entry, A140393, which gives the NQueensathome version of the sequence.  N. J. A. Sloane, Jun 18 2008
It now appears that this sequence (A000170) is correct and A140393 is wrong.  N. J. A. Sloane, Nov 08 2008
Added a(26) as calculated by Queens(AT)TUD [http://queens.inf.tudresden.de/]. Thomas B. Preusser (thomas.preusser(AT)tudresden.de), Jul 11 2009


STATUS

approved



