NQJ
      +--------
NUUNM | XJMNJYR
       -TLNTU
        =====
        NRNPNY
       -NHQWNP
        ======
         HNTQPR
        -HGWFYN
         ======
          HXNMH

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard