Project: Allow the user to input an integer, and output
a prime factor tree for that integer.
Break down the integer into smaller integers until you are left with two
primes. You can do this with a technique called recursion, which is
calling a function within that function.
In this case, the function will take an integer as a parameter, find the
first factor, and then call itself with a smaller integer. Eventually,
the function will stop calling itself when it cannot find more factors.