1,4

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Kenji Kise, Takahiro Katagiri, Hiroki Honda and Toshitsugu Yuba: Solving the 24-queens Problem using MPI on a PC Cluster, Technical Report UEC-IS-2004-6, Graduate School of Information Systems, The University of Electro-Communications (2004)

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Patrick GUILLEMIN, N-Queens Challenge [Broken link?]

Patrick GUILLEMIN, N-Queens Challenge [Broken link?]

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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 (benoit7848c(AT)orange.fr), Nov 10 2002

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

See A140393 for another version. Cf. A002562, A065256.

Adjacent sequences: A000167 A000168 A000169 this_sequence A000171 A000172 A000173

Sequence in context: A029673 A054790 A140393 this_sequence A038216 A145911 A027626

nonn,hard,nice

N. J. A. Sloane (njas(AT)research.att.com).

Terms for n=21-23 computed by Sylvain PION (Sylvain.Pion(AT)sophia.inria.fr) and Joel-Yann FOURRE (Joel-Yann.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 Yuh-Pyng (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 (njas(AT)research.att.com), May 01 2006

The NQueens-at-Home 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 NQueens-at-home version of the sequence. - N. J. A. Sloane (njas(AT)research.att.com), Jun 18 2008

It now appears that this sequence (A000170) is corrected and A140393 is wrong. - N. J. A. Sloane (njas(AT)research.att.com), Nov 08 2008