Summations that are functions of n

Question

I can't figure out how to compute the closed-form sum for this, I'm not sure which rule applies to this, and with i not at 1 or 0.

^log(n)

f(n) = ∑ (5n)

i=3

Answer 1

Again your question and/or notation is/are not clear.

Your upper limit of summation is not an integer; you index of summation does not occur in the summand.

If you can clarify your question, please comment and I will try to help further.