Is there a general expression for this pattern?

Question

I am trying to find a general expression for this pattern, I know it must be something stupidly easy but I can't seem to find it. Could somebody please help me?

Answer 1

Consider the sum of $(-1)^iI_i$ for $i = 2$ to $n-1$

Answer 2

For $n$ even, let $k=n/2$, then if you put the even terms on the left and odds on the right, it is $$\sum_{i=1}^kI _{2i}=\sum_{i=1}^kI _{2i-1}$$ For $n$ odd, increase the upper limit on the right by $1$.