He sends an e-mail to 3 of his friends (call this round 1).

Each of these friends forwards the e-mail to 3 other people (round 2).

Those 9 people each forward the e-mail to 3 other people (round 3), and so on.

Assume that nobody receives the e-mail more than once.

Determine an expression for the total number of people, including Elijah, who are aware of the good news by the nth round.

Guest Feb 28, 2021