A051758 Consider problem of placing A051755(n) queens on an n X n board so that each queen attacks precisely 2 others. Sequence gives number of solutions up to square symmetry.

1, 4, 2, 1, 1, 5, 2, 15

Offset: 2

Author

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

Keywords

• nonn
• nice
• more

Crossrefs

Cf. A051754-A051759, A051567-A051571, A019654.

Extensions

a(9) from Sean A. Irvine, Oct 05 2021