trying to prove that the sum of consecutive odd numbers is always the difference of two sqaures.

First I listed the odd numbers

1; 3; 5; 7; 9,

Then difference of two squares

4 -1 = 3

9-4 = 5

16 - 4 = 12 = 5 +7 (sum of odd numbers)

25 - 4 = 21 = 5 + 7 + 9

How do I generalise? please help.