LTPQ
      +---------
MUGMP | PUTXUWHZ
       -ZTNZW
        =====
        MNHQZW
       -MGLUWQ
        ======
         MQZTYH
        -MJHJTH
         ======
          MRPQVZ
         -MLYNYR
          ======
           MRYTN

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: challenging