A178793 These are the y coordinates of isolated visible lattice points in the plane.

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

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 * A334531 A161763 A189005

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