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 A165164 #6 May 28 2018 06:05:22 %S A165164 4,6,24,133 %N A165164 Smallest k such that no set of n lattice points gives visibility to every point of a square k X k lattice. %C A165164 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 A165164 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 A165164 Equals minimum k such that A157639(k) > n. %K A165164 hard,nonn %O A165164 1,1 %A A165164 _Jon E. Schoenfield_, Sep 06 2009