

A260320


Number of asymmetric characteristic solutions to the nqueens problem.


4



0, 0, 0, 0, 1, 0, 4, 11, 42, 89, 329, 1765, 9197, 45647, 284743, 1846189, 11975869, 83259065, 621001708, 4878630533, 39333230881, 336375931369, 3029241762900, 28439270037332, 275986675209470, 2789712437580722
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,7


COMMENTS

The problem of placing eight queens on a chessboard so that no one of them can take any other in a single move is a particular case of the more general problem: On a square array of n X n cells place n objects, one on each of n different cells, in such a way that no two of them lie on the same row, column, or diagonal.
There are no ordinary solutions for n < 5, and there is just one complete set of ordinary solutions for n = 5: 13524, 52413, 24135, 35241, 53142, 14253, 42531, 31425 (generated by reflection and rotation).
On the ordinary chessboard of 8 X 8 cells there are a total of 92 solutions, consisting of 11 sets of equivalent ordinary solutions and one set of equivalent symmetric solutions. There are no doubly symmetric solutions in this case. These sets may be generated in the ordinary case by 15863724, 16837425, 24683175, 2571384, 25741863, 26174835, 26831475, 27368514, 27581463, 35841726, 36258174 and in the symmetric case by 35281746.


REFERENCES

W. Ahrens, Mathematische Unterhaltungen und Spiele, second edition (1910), see page 231.
Maurice Kraitchik: Mathematical Recreations. Mineola, NY: Dover, 2nd ed. 1953, pp. 247255 (The Problem of the Queens).


LINKS

Table of n, a(n) for n=1..26.
P. Capstick and K. McCann, The problem of the n queens, apparently unpublished, no date (circa 1990?) [Scanned copy]
M. A. SainteLaguë, Les Réseaux (ou Graphes), Mémorial des Sciences Mathématiques, Fasc. 18, GauthierVillars, Paris, 1923, 64 pages. See p. 47.
M. A. SainteLaguë, Les Réseaux (ou Graphes), Mémorial des Sciences Mathématiques, Fasc. 18, GauthierVillars, Paris, 1923, 64 pages. See p. 47. [Incomplete annotated scan of title page and pages 1851]


FORMULA

a(n) = A002562(n) + A000170(n)/4 + A260318(n)/2 (n>1).  R. J. Mathar, Jul 24 2015


CROSSREFS

A002562 = A260318 + A260319 + A260320, A000170 = 2*A260318 + 4*A260319 + 8*A260320 (n>1).
Sequence in context: A000296 A032265 A320155 * A151273 A149271 A149272
Adjacent sequences: A260317 A260318 A260319 * A260321 A260322 A260323


KEYWORD

nonn,more


AUTHOR

N. J. A. Sloane, Jul 22 2015


EXTENSIONS

Offset corrected by Michael Somos, Jun 19 2017


STATUS

approved



