OFFSET
1,2
COMMENTS
Sequence A141247 gives the minimum number of points visible from a point. By symmetry, when a(n) is odd, the central point in the lattice can see only the minimal number of points. When a(n)=1, the central point is the only such point. See A141249 for the n X n lattices that have such a central point.
LINKS
T. D. Noe, Table of n, a(n) for n=1..1000
MATHEMATICA
Table[mn=n^2+1; pts=0; Do[cnt=0; Do[If[GCD[c-a, d-b]<2, cnt++ ], {a, n}, {b, n}]; If[cnt<mn, mn=cnt; pts=1, If[cnt==mn, pts++ ]], {c, n}, {d, n}]; pts, {n, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Jun 17 2008
STATUS
approved