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A178794
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These are the x coordinates of the isolated visible lattice points in the plane.
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2
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21, 99, 115, 369, 495, 475, 195, 259, 265, 225, 375, 741, 741, 649, 323, 377, 399, 1001, 1001, 441, 987, 609, 755, 1001, 545, 645, 1035, 407, 1275, 153, 645, 1275, 51, 1221, 485, 35, 805, 715, 441, 595, 1015, 221, 1001, 1183, 371, 391, 575, 519, 645, 1065
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OFFSET
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1,1
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COMMENTS
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An isolated lattice point is surrounded (in a Moore neighborhood) by 8 points that are not visible from the origin. I have also submitted the corresponding sequence of denominators.
Contribution from Gregg Whisler, Jun 21 2010: (Start)
These are also the x coordinates of the isolated visible lattice points in Z^2. (End)
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LINKS
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MATHEMATICA
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Table[Replace[Select[First/@Position[Partition[CoPrimeQ[n, Range[n]], 3, 1], {False, True, False}, {1}]+1, Outer[CoPrimeQ, n+ {-1, 1}, #1+{-1, 0, 1}]=={{False, False, False}, {False, False, False}}&], {{}-> Sequence[], list_:->Sequence@@ ({#1, n}&)/@list}], {n, 5000}]] program by Eric Rowland
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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More terms (until the initial 21 repeats) from Gregg Whisler, Jun 21 2010
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STATUS
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approved
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