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%I #6 May 28 2018 06:05:22
%S 4,6,24,133
%N Smallest k such that no set of n lattice points gives visibility to every point of a square k X k lattice.
%C At least n+1 lattice points must be selected as viewpoints in order to give visibility to all lattice points of a square a(n) X a(n) lattice.
%e For k < 24, given a k X k square lattice, there is at least one way to select a set of 3 or fewer lattice points as viewpoints that, collectively, give visibility to all k^2 lattice points; at k=24, however, no such set of 3 points exists, so a(3)=24.
%Y Equals minimum k such that A157639(k) > n.
%K hard,nonn
%O 1,1
%A _Jon E. Schoenfield_, Sep 06 2009
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