A051759 Consider the problem of placing A051756(n) queens on an n X n board so that each queen attacks precisely 3 others. Sequence gives number of solutions up to square symmetry.

1, 2, 4, 31, 307, 2, 9, 755

Offset: 2

Author

Robert Trent (trentrd(AT)hotmail.com), Aug 23 2000

Keywords

• nonn
• nice
• more

Comments

A051569 (taken from the Martin Gardner references) is another version of this sequence. - N. J. A. Sloane, May 22 2014

References

• M. Gardner, The Last Recreations, Springer, 1997, p. 282.
• M. Gardner, The Colossal Book of Mathematics, 2001, p. 209.

Links

• Erich Friedman, Illustration of initial terms
• Sean A. Irvine, Java program (github)

Crossrefs

Cf. A051754-A051758, A051567-A051571, A019654.

Extensions

a(8)-a(9) from Sean A. Irvine, Oct 01 2021