NVHW
      +---------
UNPQV | TNNQTHUN
       -UNPQV
        =====
        NPMJYH
       -NULGRQ
        ======
         ZXNXWU
        -ZQQTYY
         ======
          MUNHNN
         -MJYGWX
          ======
           YQGXL

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard