OFFSET
1,1
COMMENTS
At least n+1 lattice points must be selected as viewpoints in order to give visibility to all lattice points of a square a(n) X a(n) lattice.
EXAMPLE
For k < 24, given a k X k square lattice, there is at least one way to select a set of 3 or fewer lattice points as viewpoints that, collectively, give visibility to all k^2 lattice points; at k=24, however, no such set of 3 points exists, so a(3)=24.
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Jon E. Schoenfield, Sep 06 2009
STATUS
approved