gistfile1.clj

(defn hexstr1
  [bytes]
  (loop [cnt 0
         mybytes (seq bytes)
         hexstr ""]
    (if (seq mybytes)
      (cond
       (= (mod (inc cnt) 24) 0) (recur (inc cnt) mybytes (str hexstr "\n"))
       (= (mod (inc cnt) 12) 0) (recur (inc cnt) mybytes (str hexstr "  "))
       (= (mod (inc cnt) 3) 0) (recur (inc cnt) mybytes (str hexstr " "))
       :else (recur (inc cnt) (rest mybytes) (str hexstr (format "%02X" (first mybytes)))))
      hexstr)))

;; running (println (hexstr1 (range 1 33))) gives:
;;
;; 0102 0304 0506 0708  090A 0B0C 0D0E 0F10
;; 1112 1314 1516 1718  191A 1B1C 1D1E 1F20

(defn hstr                                                                      
   [bytes]                                                                       
   (let [f #(format "%02X" %)                                                    
         h (map f bytes)                                                         
         s (interpose \space  (partition-all 2 h))    ; thanks TimMc for \space
         s2 (interpose \space  (partition-all 8 s))
         s3 (interpose \newline (partition-all 4 s2))]
     (apply str (flatten s3))))