TXTY
      +---------
TRUJJ | YXRNRFER
       -LGRLP
        =====
          GLLFE
         -LGRLP
          =====
          HYRLTR
         -HJHHYF
          ======
           THNFG

base: 13
letters: EFGHJLNPRTUXY
difficulty: medium
restrictions: no multiplication