MTH
      +--------
GLQUP | HTMPUJP
       -LPRNQ
        =====
        GMHMWJ
       -GNUPJH
        ======
          WJTNP
         -WLNRN
          =====
           MWLM

base: 13
letters: GHJLMNPQRTUWY
difficulty: hard
missing: Y