Can someone help me with this summation?

Question

http://tinyurl.com/yf8ubf

It can be found here.

I have a feeling that i=4 has something to do with this odd problem.

Answer 1

The summation formula you used before,

4n(n+1)/2 - 5n,

sums 4x-5 from 1 to 33, giving you 2079.

You want to sum from 4 to 33, so you need to subtract off the terms corresponding to 1,2,3. That is, you want

4n(n+1)/2 - 5n - [ 4k(k+1)/2 - 5k ]

where n=33, and k=3.