A chain letter works as follows: One person sends a copy of the letter to five friends
Chapter 5, Problem 24(choose chapter or problem)
A chain letter works as follows: One person sends a copy of the letter to five friends, each of whom sends a copy to five friends, each of whom sends a copy to five friends, and so forth. How many people will have received copies of the letter after the twentieth repetition of this process, assuming no person receives more than one copy?
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