JYGR
      +---------
NNGMR | XUWYPQWZ
       -NNGMR
        =====
        GRTHTQ
       -GXXVLR
        ======
          QHJXW
         -UUMHR
          =====
          HLTLJZ
         -HHJYUV
          ======
           GNXLZ

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium