More information is needed here. Specifically, you have to make assumptions about and
I assume you want g to be constant and where i is a constant?
if so, and assuming you are at time 0, and dividends are payable once per period starting at time 1, and assuming dividends grow at the constant rate g you can write:
Div = the first dividend payment (I've assumed this happens at time 1)
g = the constant growth rate of dividends
You can recognise this as a geometric progression. The sum is then;
You should be able to simplify and rearrange this for
Then you have from our assumption