num_fac.clj

(defn fac [n]
  (loop [n n, acc 1]
    (if (zero? n)
      acc
      (recur (dec n) (* acc n)))))

(fac 20)
; => 2432902008176640000
(fac 25)
; => java.lang.ArithmeticException: integer overflow

(fac 20N)
; => 2432902008176640000
(fac 25N)
; => 7034535277573963776
(fac 26N)
; => -1569523520172457984

(defn fac [n](loop [n n, acc %28num 1%29]
%28if %28zero? n%29
acc
%28recur %28dec n%29 %28* acc n%29%29%29))