I have to calculate a series but since the `Sigma`

icon represents ALL possible formulas in the UI, it’s very difficult to find a documentation on the actual "mathematical" summation symbol.

Let’s say I want to calculate something like the growth of an hypothetical animal that weighs 200g over 3 years.

My mathematical notation would be the following

But I don’t know how to represent that in Google Sheets. What I did find was `SERIESSUM`

however the documentation left me with more question than answers, I’m not sure if the "power sum" they mention is what I am looking for.