OFFSET
0,3
COMMENTS
Sequence A115993 is an upper bound to this sequence. I do not know whether the two sequences differ.
LINKS
EXAMPLE
a(3)>=4 because we can place 4 queens on a cubic chessboard, as follows: S = {(0,0,0), (1,2,0), (0,1,2), (2,0,1)}. A further queen cannot be placed at (1,0,2), for instance, because that position is attacked by (2,0,1) (and also, incidentally, by (1,2,0) and (0,1,2), but not by (0,0,0)).
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Frederic van der Plancke (fplancke(AT)hotmail.com), Feb 10 2006, Feb 15 2008
STATUS
approved