Hey I need help

Hey, so upon first looking at this question, I recognize that you may have to calculate f(2) then f(3) then f(4) and keep on going until you reach f(10). This is the easiest way that I can think of solving it. 

SOMEONE REALLY NEEDS TO CONFIRM THIS STATEMENT BECAUSE I AM SUPER NOT 100%SURE ABOUT IT.

f(10) is a very large number.  By writing a simple recursion routine in software I find f(10) is approximately equal to 2.972x10¹¹⁷.

I wouldn't want to try to calculate this by hand!