When j = n - 3, what is the simplified form of n + j - 5?
If you can simplify "n + j - 2" to be something simpler, why not?
= 2 * ( (n-2) + (n-1) + n +... + (2n-5) )
...
I don't understand where the (2n-5) comes from in line 2, and then why we use it in the summation on line 3. Nor do I understand where those summations come from on line 3 and why we subtract them.