RUPE
      +---------
PARRF | QUNMRPNF
       -PARRF
        =====
         AAUMPN
        -AMAQEE
         ======
          MHHHEF
         -MMAEAP
          ======
           RFUQM

base: 10
letters: AEFHMNPQRU
difficulty: hard
restrictions: no multiplication