Clojure code to generate the nth Fibonacci number using a formula.

fibonacci_formula.clj

(require '[clojure.math.numeric-tower :as math])

(defn fibonacci
  "Returns the nth Fibonacci number by using the Golden Ratio formula."
  [n]
  (let [root-five (math/sqrt 5M)
        golden-ratio (/ (+ 1 root-five) 2)]
    (math/round (bigdec (/ (math/expt golden-ratio n)
                           root-five)))))