summation over many i's

[tugo]

Good Afternoon.

I want to do the following calculation on excel: Xn=(Sum from 0 to n) B^(n-i)*Yi.
I know it's messy but (Sum from 0 to n) its like the summation sign from 0 until n, changing i and as a consequence, it will also change Yi and n may also be large.
Ps: i already have calculated all Yi's ad have the B.

I hope you guys can help.
Thank you.

[ChemistB]

First, I put B in B1 and n in B2. I put Yi in A2:A21 so n has a maximum of 20 in my sheet.

To make the formula easier to follow, first I made 2 defined names
Is =ROW(Sheet1!$A$1:INDEX(Sheet1!$A$1:$A$20, Sheet1!$B$2))
Yis = =Sheet1!$A$2:INDEX(Sheet1!$A$2:$A$21,Sheet1!$B$2)

"Is" simplifies to the numbers from 1 to n
"Yis" adjusts to the specific Yi's based on what n is (B2)

Then the formula (in C2) is simply

=SUMPRODUCT($B$1^($B$2-Is)*ysi)

I put the individual i calculations in column E to test it.