QHJ
      +---------
XFFPG | UMFGXRWH
       -UJFURE
        ======
         NFXNPW
        -RPFRUU
         ======
          NXUJQH
         -NNFREM
          ======
           NUQNJ

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