AAA
      +---------
6B9BB | 6B982331
       -6CC7AC
        ======
         67B2A3
        -6CC7AC
         ======
          666AA1
         -6CC7AC
          ======
           22C93

base: 13
letters: 0123456789ABC
difficulty: hard
restrictions: one multiplication
hints: 0 < 2, 8 = 1 * 1, 5 << 4
missing: 4 5 0