FUUY
      +---------
FJPFG | FWUYFFMJ
       -FJPFG
        =====
         URRNF
        -UFNUM
         =====
          UHYRM
         -UFNUM
          =====
           YMUJJ
          -YGFHR
           =====
            GJRN

base: 13
letters: FGHJLMNPQRUWY
difficulty: intermediate
restrictions: no multiplication
missing: Q L