

A006717


Number of ways of arranging 2n+1 nonattacking semiqueens on a (2n+1) X (2n+1) toroidal board.
(Formerly M3005)


5



1, 3, 15, 133, 2025, 37851, 1030367, 36362925, 1606008513, 87656896891, 5778121715415, 452794797220965, 41609568918940625
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OFFSET

0,2


COMMENTS

Also the number of "good" permutations on 2n+1 elements [Novakovich].  N. J. A. Sloane, Feb 22 2011
Also the number of transversals of a cyclic Latin square of order 2n+1 and the number of orthomorphisms of the cyclic group of order 2n+1.  Ian Wanless, Oct 07 2001
Also the number of complete mappings of a cyclic group of order 2n+1; also (2n+1) times the number of "standard" complete mappings of cyclic group of order 2n+1.  Jieh Hsiang, D. Frank Hsu and Yuh Pyng Shieh (arping(AT)turing.csie.ntu.edu.tw), May 08 2002
See A003111 for further information.
A very simple model using only addition mod n: Let i=index vector (0,1,..n1) on any set of n distinct values, and j=index vector for the values after reordering. Then j=(i + d) mod n, where d is the vector of distances moved, and a(n) = number of reorderings that give an equidistributed set d (i.e., 1 instance of each distance moved). Since a(n)=0 for all even n, taking only odd n gives the sequence above  Ross Drewe, Sep 03 2017


REFERENCES

N. Yu. Kuznetsov, Using the Monte Carlo Method for Fast Simulation of the Number of "Good" Permutations on the SCIT4 Multiprocessor Computer Complex, Cybernetics and Systems Analysis, January 2016, Volume 52, Issue 1, pp 5257.
D. Novakovic, (2000) Computation of the number of complete mappings for permutations. Cybernetics & System Analysis, No. 2, v. 36, pp. 244247.
Yuh Pyng Shieh, Jieh Hsiang and D. Frank Hsu, On the enumeration of Abelian kcomplete mappings, vol. 144 of Congressus Numerantium, 2000, pp. 6788
Yuh Pyng Shieh, Partition Strategies for #Pcomplete problem with applications to enumerative combinatorics, PhD thesis, National Taiwan University, 2001
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
I. Vardi, Computational Recreations in Mathematica. AddisonWesley, Redwood City, CA, 1991, p. 118.


LINKS

Table of n, a(n) for n=0..12.
N. J. Cavenagh and I. M. Wanless, On the number of transversals in Cayley tables of cyclic groups, Disc. Appl. Math. 158 (2010), 136146.
V. Kotesovec, Nonattacking chess pieces, 6ed, 2013
B. D. McKay, J. C. McLeod and I. M. Wanless, The number of transversals in a Latin square, Des. Codes Cryptogr., 40, (2006) 269284.
Kevin Pratt, ClosedForm Expressions for the nQueens Problem and Related Problems, arXiv:1609.09585 [cs.DM], 2016.
D. S. Stones and I. M. Wanless, Compound orthomorphisms of the cyclic group, Finite Fields Appl. 16 (2010), 277289.
Eric Weisstein's World of Mathematics, Queens Problem.


FORMULA

Suppose n is odd and let b(n)=a((n1)/2). Then b(n) is odd; if n>3 and n is not 1 mod 3 then b(n) is divisible by 3n; b(n)=2n mod n^2 in n is prime; b(n) is divisible by n^2 if n is composite; b(n) is asymptotically in between 3.2^n and 0.62^n n!. [Cavenagh, Wanless], [McKay, McLeod, Wanless], [Stones, Wanless]  Ian Wanless, Jul 30 2010


PROG

(MATLAB) k = 6; A = zeros(1, k); for i = 1:k; n = 2*i1; x = [0: n1]; allP = perms(x); T = size(allP, 1); X = repmat(x, T, 1); Y = mod(X + allP, n); Y = sort(Y, 2); L = ~(sum(Y ~= X, 2)); A(i) = sum(L); end; A
% 1st 6 terms by testing all n! possible distance vectors
% Ross Drewe, Sep 03 2017


CROSSREFS

Cf. A003111, A007705.
Sequence in context: A222390 A281186 A108210 * A222263 A246804 A230166
Adjacent sequences: A006714 A006715 A006716 * A006718 A006719 A006720


KEYWORD

nonn,more,nice


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from Jieh Hsiang, D. Frank Hsu and Yuh Pyng Shieh (arping(AT)turing.csie.ntu.edu.tw), May 08 2002
a(12) added from A003111 by N. J. A. Sloane, Mar 29 2007
Definition clarified by Vaclav Kotesovec, Sep 16 2014


STATUS

approved



