Thane Plambeck  wrote on 06/27/2004, about "Knuth Vol 4" preview material:

Here's a puzzle from it [rated 25 on the Knuth scale]
What is the 7.2.1.2.26:  What is the unique alphametic solution to
NIIHAU \pm KAUAI \pm OAHU \pm MOLOKAI \pm LANAI \pm MAUI \pm HAWAII = 0?
(\pm : "plus or minus")

This is an especially nice puzzle, because there is also a (different) unique answer if  the "= zero"
is mis-read as "= the letter O".

-- Mike