This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A178794 #14 Jul 12 2025 08:36:48
%S A178794 21,99,115,369,495,475,195,259,265,225,375,741,741,649,323,377,399,
%T A178794 1001,1001,441,987,609,755,1001,545,645,1035,407,1275,153,645,1275,51,
%U A178794 1221,485,35,805,715,441,595,1015,221,1001,1183,371,391,575,519,645,1065
%N A178794 These are the x coordinates of the isolated visible lattice points in the plane.
%C A178794 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.
%C A178794 From _Gregg Whisler_, Jun 21 2010: (Start)
%C A178794 a(n) is also A157429 + 1.
%C A178794 These are also the x coordinates of the isolated visible lattice points in Z^2. (End)
%H A178794 Eric W. Weisstein, <a href="https://mathworld.wolfram.com/VisiblePoint.html">MathWorld: Visible Point</a>
%t A178794 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,2000}][[All, 1]] (* _Eric Rowland_ *)
%Y A178794 Cf. A178793 (corresponding y coordinates), A157428, A157429, A216467.
%K A178794 nonn
%O A178794 1,1
%A A178794 _Gregg Whisler_, Jun 15 2010
%E A178794 More terms (until the initial 21 repeats) from _Gregg Whisler_, Jun 21 2010