Number of Squares in an N * N Grid

Create a function that calculates the number of different squares in an n * n square grid.

Examples

number_squares(2) ➞ 5

number_squares(4) ➞ 30

number_squares(5) ➞ 55

Explanation

• If n = 0 then the number of squares is 0
• If n = 1 then the number of squares is 1 + 0 = 1
• If n = 2 then the number of squares is 2^2 + 1 = 4 + 1 = 5
• If n = 3 then the number of squares is 3^2 + 5 = 9 + 5 = 14

As you can see, for each value of n the number of squares is n squared + the number of squares from the previous value of n.

Notes

• Input is a positive integer.
• Square pyramidal number.