Clojure: Number divisible by eleven

eleven.clj

(defn string-to-number [number-string]
  (let [convert (int \0)]
    (map #(- (int %) convert) number-string)))

(defn map-by-index [numbers]
  (map-indexed #(if (even? %1) %2 (- %2)) numbers))

(defn divide-even? [number-string]
  (= 0 (mod (reduce + 0 (map-by-index (string-to-number number-string))) 11)))

(loop [user-input (read-line)]
  (when (not= user-input "0")
    (println (if (divide-even? user-input) "SIM" "NAO"))
    (recur (read-line))))