How to create a loop formula

Hi,

I just came across array formulas today, don't know why I haven't realised this possibility yet. And not really sure I understand the use of them yet either, but I am trying to read up on it.

Anyway, I have an issue which I'm unsure can be fixed with the use of arrays or nto.

I have a formula, which tells the numbers of reinvestments needed. from 1 to more. Result of this is "number_of_reinvestments".


Then I have a formula which is =NPV(5%;year*number_of_reinvestments;0;-100)

I need the above formula to be done once for each reinvestment necessary. So if "number_of_reinvestments" = 2 then the formula would be like this

=NPV(5%;year*1;0;-100)+NPV(5%;year*2;0;-100)

How can I write the formula above so that it would expand depending on the "number_of_reinvestment"?