Answer:
n = 9
Explanation:
Let's first prove that for any constants k > 0,


The derivative

and the derivative

Now, applying L'Hôpital's rule we find that

Now, let f be the function

It is easy to see that f(x) is
only if

If

but both n-8 and n-6 are greater than one, so

and f is

On the other hand, if
then

but 8-n is greater or equal than one, so

and so f(x) in not
