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A178793 These are the y coordinates of isolated visible lattice points in the plane. 3
55, 175, 551, 575, 589, 609, 679, 741, 741, 791, 799, 805, 875, 945, 987, 987, 995, 1035, 1065, 1105, 1105, 1159, 1209, 1275, 1309, 1309, 1309, 1407, 1421, 1463, 1463, 1463, 1495, 1495, 1551, 1581, 1581, 1611, 1625, 1639, 1651, 1665, 1665, 1665, 1695 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Contribution from Gregg Whisler, Jun 21 2010: (Start)

a(n) is also A157428 + 1. [Charles R Greathouse IV points out that this is false, since (1308, 1274) is in (A157428, A157429) but not in (A178793, A178794). Oct 17 2012]

An isolated lattice point is surrounded (in a Moore neighborhood of r=1) in the Z^2 lattice of points by 8 points that are not visible from the origin.

(End)

LINKS

Table of n, a(n) for n=1..45.

Eric W. Weisstein, Visible Point

MATHEMATICA

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}]] (* Eric Rowland *)

CROSSREFS

Cf. A157428, A157429, A178794 (corresponding x coordinates), A216467.

Sequence in context: A068641 A039781 A135657 * A161763 A189005 A105442

Adjacent sequences:  A178790 A178791 A178792 * A178794 A178795 A178796

KEYWORD

nonn

AUTHOR

Gregg Whisler, Jun 15 2010

EXTENSIONS

More terms (until the corresponding first x coordinate (21) repeats) from Gregg Whisler, Jun 21 2010

STATUS

approved

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Last modified April 9 06:32 EDT 2020. Contains 333343 sequences. (Running on oeis4.)