How to obtain the power series of finite power sum?

Questions
1

Is there anybody can help me to get an expansion for the following finite Power Sum?

(Sum[(\[Beta]*x)^i/i!, {i, 0, m - 1}])^n

As I know the infinite power sum can be expressed as follows

powersum.jpg
powersum.jpg528×180 11 KB

but what about the case of finite power sum?

Thanks for your support

2 
I get the following result using Mathematica 9:

In[1]:= (Sum[(\[Beta]*x)^i/i!, {i, 0, m - 1}])^n


Out[1]= ((E^(x \[Beta]) Gamma[m, x \[Beta]])/Gamma[m])^n

S M Blinder

3

Thanks for your reply, but I need to get a result in summation form, and Not in Gamma function.