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A141248
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Number of points having minimal visibility in a square n X n lattice of points.
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3
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1, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 36, 1, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 9, 4, 4, 52, 4, 4, 8, 4, 4, 44, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 12, 4, 4, 4, 4, 1, 4, 4, 4, 4, 4, 4, 4, 1, 4, 4, 4, 20, 4, 4, 4, 4, 8, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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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.
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1000
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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}]
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CROSSREFS
| Cf. A141225.
Sequence in context: A010709 A138908 A032564 * A088899 A066014 A080678
Adjacent sequences: A141245 A141246 A141247 * A141249 A141250 A141251
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KEYWORD
| nonn
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AUTHOR
| T. D. Noe (noe(AT)sspectra.com), Jun 17 2008
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