JRX
      +--------
JNWWV | JVPTYRH
       -JNWWV
        =====
         UUQGR
        -MRLGU
         =====
         JGZHXH
        -JJPYWP
         ======
           XGVR

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard