1644
      +---------
618C9 | 1A8ABCD1
       -17463
        =====
         6AD3C
        -618C9
         =====
          4E78D
         -4FB02
          =====
           4C3F1
          -4FB02
           =====
            66B7

base: 16
letters: 0123456789ABCDEF
difficulty: hard
missing: 5