21C2
      +---------
78407 | 5C847275
       -00C41
        =====
        4045C2
       -4114AA
        ======
         496247
        -4B6594
         ======
           52145
          -00C41
           =====
           4C432

base: 13
letters: 0123456789ABC
difficulty: medium
missing: 3