closed form for T(n) = c^n + T(n-1)

Hi all.

I recently came across a recurrence of the form:

T(0) = a
T(n) = c^n + T(n-1)

Of course, when c is 2, T(n) = (a)*2^n. But, is there a general closed form for arbitrary c, or at least for when c is an arbitrary positive integer?

Thanks in advance for any response. -Dan
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