Nilakantha's series for calculating π

pi.clj

(defn nilakantha [iterations]
  (loop [sum 3.0M
         counter 0
         sign +]
    (if (>= counter (* 2 iterations))
      sum
      (recur
       (sign sum 
             (/ 4.0M
                (* (+ counter 2)
                   (+ counter 3)
                   (+ counter 4))))
       (+ counter 2)
       (if (= sign +) - +)))))

(println
 (with-precision 10000
   (nilakantha 150)))