What's sum of series of increasing powers?

[Tad Dunne]

Help!

I'm working on an Excel spreadsheet and need a formula or function that
will give,

for an input A and B,   the sum of all the powers of A for integers from
1 to B.
Example:  1.05 + 1.05 squared + 1.05 cubed ...

Can anyone help me?

-- Tad Dunne