Rosen-Counting

Question

Once a computerworm infects a personal computer via an
infected e-mail message, it sends a copy of itself to 100 email
addresses it finds in the electronic message mailbox
on this personal computer. What is the maximum number
of different computers this one computer can infect in the
time it takes for the infected message to be forwarded five
times?

I wanted to verify this answer and method,there is no answer given for this question.

Comments

The infection would represent a tree whose fan-out is 100 with height 5

If x=100, then 

#infected computers = 1+x+x²....+x⁵

Is it correct?

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I have thought exactly the same way, like the tree structure with 100 nodes each level.I think it is correct,solution or answer not given for this question.thanks!