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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.
2
1, 4, 2, 1, 1, 5, 2, 15
OFFSET
2,2
CROSSREFS
KEYWORD
nonn,nice,more
AUTHOR
Robert Trent (trentrd(AT)hotmail.com), Aug 23 2000
EXTENSIONS
a(9) from Sean A. Irvine, Oct 05 2021
STATUS
approved