Here is a puzzle that's simple to state but not so easy to solve. Take a set of English Scabble tiles with its standard complement of 98 letters and two blanks (that can be used to stand for any letter). Use all 100 tiles to make a list of names of countries in the world, all different. For the acceptable list of country names use the current list of 192 member states of the United Nations.
"Spanning the Globe With Scrabble Tiles,"
Word Ways: Vol. 45
, Article 5.
Available at: http://digitalcommons.butler.edu/wordways/vol45/iss2/5