A051567 Consider problem of placing N queens on an n X n board so that each queen attacks precisely k others. Here k=1 and sequence gives number of inequivalent solutions when N is equal to the upper bound 2*floor(2n/3).

0, 5, 0, 2, 149, 49, 1, 12897, 2238, 109, 2606412, 450118, 17579

Offset

3,2

Comments

a(n) = 0 if N does not achieve 2*floor(2n/3).

References

Martin Gardner, The Last Recreations, Springer, 1997, p. 282.

Martin Gardner, The Colossal Book of Mathematics, 2001, p. 209.

Links

Table of n, a(n) for n=3..15.

Martin Gardner, The Last Recreations, 1997

Vaclav Kotesovec, The unique solution for chessboard 9 X 9

Manfred Scheucher, C Code

Crossrefs

Cf. A051568-A051571, A051754-A051759, A019654.

The number of solutions when N takes its maximal value is A051757.

Sequence in context: A190913 A019106 A051566 * A361980 A355068 A261219

Adjacent sequences: A051564 A051565 A051566 * A051568 A051569 A051570

Keyword

nonn,more,nice

Author

N. J. A. Sloane

Extensions

Description corrected by and one more term from Jud McCranie, Aug 25 2001

a(12)-a(15) from Martin Fuller, Dec 22 2025

Status

approved