the other way

0 is the center square of nine which define a larger square, which we'll call 1.

Those nine squares are 1.1 - 1.9, and 1.5 is square 0.

1 is the center square of nine which define a larger sqaure which we'll call 2.

Those nine squares are called 2.1 - 2.9 with 1 being 2.5.

It goes on to infinity.