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%I #9 Dec 06 2014 01:35:33
%S 1,4,9,13,19,25,35,43,55,65,81,91,111,125,147,163,187,203,233,251,283,
%T 305,337,359,399,422,465,491,531,553,609,636,691,721,769,799,863,896,
%U 961,993,1051,1085,1159,1199,1267,1313,1377,1416,1501,1547,1627,1679
%N Maximum number of points visible from some point in a square n X n lattice.
%C Two points (a,b) and (c,d) are visible to each other when gcd(c-a,d-b)=1. Sequence A141225 gives the number of lattice points that have maximal visibility.
%H T. D. Noe, <a href="/A141224/b141224.txt">Table of n, a(n) for n=1..1000</a>
%H Eric Weisstein, <a href="http://mathworld.wolfram.com/VisiblePoint.html">MathWorld: Visible Point</a>
%F The maximum number of visible points is slightly more than c*n^2, with c = 6/Pi^2.
%t Table[mx=0; Do[cnt=0; Do[If[GCD[c-a,d-b]<2, cnt++ ], {a,n}, {b,n}]; If[cnt>mx, mx=cnt], {c,n}, {d,n}]; mx, {n,20}]
%K nice,nonn
%O 1,2
%A _T. D. Noe_, Jun 15 2008
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