6751
      +---------
C2147 | 3C411966
       -C2147
        =====
        645C69
       -6A4470
        ======
         C42156
        -C36A96
         ======
          693AB6
         -67688A
          ======
           CCAB5

base: 13
letters: 0123456789ABC
difficulty: medium