16CD
      +---------
3C57B | E31D3C2B
       -3C57B
        =====
         2667C
        -57289
         =====
          54AC2
         -BC1C0
          =====
          3EB90B
         -330290
          ======
           13E0E

base: 15
letters: 0123456789ABCDE
difficulty: medium