(defn sq[n]
  (loop [candidate (/ n 2.0)
         prev-candidate (double n)]
      (let [step (/ (abs (- prev-candidate candidate)) 2)
            square (* candidate candidate)
            epsilon (abs (- n square))]
        (if (< epsilon 0.001) (round candidate)
          (if (> square n) (recur (- candidate step) candidate) (recur (+ candidate step) candidate))))))

(fact (sq 4) => 2)
(fact (sq 16) => 4)
(fact (sq 9) => 3)
(fact (sq 49) => 7)