João's functional equation
Let \( f \) be a function from the positive integers to the positive integers that satisfies the property \[ f (x + y) = f (x) f (y) \]
for all pairs of positive integers \((x,y) \). If we are given that \( f(2) = 9 \), what is the value of \( f(5) \)?
This problem is posed by João B.