In the square network of 1x 1, there are 1 squares (the side length is 1).

In a 2×2 square network, there are 1 squares (side length is 2)+2 squares (side length is 1).

In a 3×3 square network, there are 1 square (side length 3)+2 squares (side length 2)+3 squares (side length 3).

And so on, another one, you see, how many squares does nxn's square network have, from the square of 1 to the square of N.