CUSIP check digit -- http://en.wikipedia.org/wiki/CUSIP

cusip.clj

(def lookup-int-val
  (merge
   {\* 36 \@ 37 \# 38}
   (zipmap (map char(range 48 58)) (range))
   (zipmap
    (map char (range 65 91))
    (drop 10 (range)))))

(defn inc-sum [sum v i]
  (let [val (if (even? i) (* 2 v) v)]
    (+ sum
       (int (/ val 10))
       (mod val 10))))

(defn compute-sum [cusip]
  (loop [sum 0
         i 1
         xs (take 8 (clojure.string/upper-case cusip))]
    (let [v (get lookup-int-val (first xs))]
      (if (nil? v)
        sum
        (recur (inc-sum sum v i) (inc i) (rest xs))))))

(defn cusip-check-digit [cusip]
  (mod (- 10 (mod (compute-sum cusip) 10)) 10))

;;(cusip-check-digit "912828NB2")
;;=>2