[seqfan] duplicate sequence related to set covering on a square grid
Rob.Pratt at sas.com
Wed Oct 2 05:18:06 CEST 2013
It looks like:
Given n^2 points forming a square grid, a(n) is the minimum number of points to be removed from the grid, so that, if 4 of the remaining ones are chosen, they do not form a square with sides parallel to the grid.
0, 1, 2, 4, 8, 12, 17, 23, 30, 39 (list<http://oeis.org/A227112/list>; graph<http://oeis.org/A227112/graph>; refs<http://oeis.org/search?q=A227112+-id:A227112>; listen<http://oeis.org/A227112/listen>; history<http://oeis.org/history?seq=A227112>; text<http://oeis.org/search?q=id:A227112&fmt=text>; internal format<http://oeis.org/A227112/internal>)
is a newer and more complete version of:
On a 4 X 4 square grid, there are 14 lattice squares parallel to the axes. What is the fewest dots you can remove from the grid such that at least one vertex of each of the 14 squares is removed? The answer is a(4) = 4. In general a(n) is the answer for an n X n grid.
0, 1, 2, 4, 8, 12, 17 (list<http://oeis.org/A152125/list>; graph<http://oeis.org/A152125/graph>; refs<http://oeis.org/search?q=A152125+-id:A152125>; listen<http://oeis.org/A152125/listen>; history<http://oeis.org/history?seq=A152125>; text<http://oeis.org/search?q=id:A152125&fmt=text>; internal format<http://oeis.org/A152125/internal>)
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