A152125 - cp's OEIS frontend

A152125 Consider a square grid with side n consisting of n^2 cells (or points); a(n) is the minimal number of points that can be painted black so that, out of any four points forming a square with sides parallel to the sides of the grid, at least one of the four is black.

n	a(n)
1	0
2	1
3	2
4	4
5	8
6	12
7	17
8	23
9	30
10	39
11	48
12	59
13	71

[0, 1, 2, 4, 8, 12, 17, 23, 30, 39, 48, 59, 71]