Answer:
;

Explanation:
Given

Every other minute

Required
Determine the recursive function
Let the number of minutes be represented with n.
The initial condition can be represented as:

--- i.e. 3 friends initially at the first minute
At every other minutes:
i.e 2 minutes upwards
This means that n follows the following sequence

Note that the difference between each term is 1.
This means that recursive function has to be defined backwards i.e.

Where k = 2
i.e. The number of friends that received the video from each friend
So, we have:

Hence, the recursive function is:
;
