Consider the set S(r) of points (x,y) with integer coordinates satisfying |x| + |y|
Let O be the point (0,0) and C the point (r/4,r/4).
Let N(r) be the number of points B in S(r), so that the triangle OBC has an obtuse angle, i.e. the largest angle α satisfies 90°
So, for example, N(4)=24 and N(8)=100.
What is N(1,000,000,000)?