A quick & dirty number to string packing implementation

pack_number.clj

(import '[java.util Random])
(def ^:const seed 42)
(def ^Random shuffler (Random. seed))
(def alphabet (->> "abcdefghijklmnopqrstuvwxyz0123456789"
                    (sort-by (fn [_] (.nextInt shuffler)))
                    vec))
(def N (count alphabet))
(defn pack-number
  ([n] (pack-number n ""))
  ([n buf]
    (let [n-rem (rem n N)
          n-quot (quot n N)
          buf (str buf (nth alphabet n-rem))]
      (if (zero? n-quot)
        buf
        (recur n-quot buf)))))

(defn unpack-number
  [buf]
  (reduce #(+ %2 (* N %1)) 0 (map #(.indexOf alphabet %) (reverse buf))))

(pack-number 42)
(unpack-number "lc")

(assert (= (unpack-number (pack-number 42)) 42))