9712
      +---------
167A1 | AC314551
       -167A1
        =====
        97B6B5
       -971409
        ======
          74775
         -3B95A
          =====
          1134A1
         -188863
          ======
           1363B

base: 13
letters: 0123456789ABC
difficulty: intermediate
missing: 2