One of my equations is unstable in massive for loop

Sorry for the confusing wording, but I will explain the best I can. In my code I am outputing a matrix using two for loops. However, the last element has to be added seperately because it tries to pull an elemnt outside the array size. But after about 30 loops the last number starts straying from 25 even though it should stay consistently at 25 for awhile. Im not sure why the equation is unstable and could use some help. I attatched screenshots of the code. Sorry if this is hard to understand but I would greatly appreciate help!!

[Geoff Hayes]

Maxwell - please attach your code rather than screenshots of the code. Also include instructions on how you can call it (including input parameters).