Knuth's up-arrow notation

(defun knuth (x n)
  (if (= n 2)
      (return-from knuth (expt x x))
    (return-from knuth (expt x (knuth x (- n 1))))
    )
)


Yes, an implementation in 6 lines of Lisp. What is Knuth's up-arrow notation? Wikipedia that shit. Don't try this with anything greater than (knuth 3 3), or you will overflow. (knut 3 3) == 3^3^3. (knuth 3 4) == 3^3^3^3.

Even fagget liek me knows how to do n00b things like this with recursion in fucking every language.  Just like crappy C's version which is shorter
int knuth(int a, int b)
{
  if (b == 2) return a * a; else knuth(a, b - 1);
}