A recent Word Ways article, "Sudoku Patterns" (May 2007), explored aspects of sudoku squares which employ letters instead of numbers. One highlighted aspect of the article was theme sudokus. Two examples of theme sudokus were puzzles in which various number names were hidden.
"Compass Point Sudokus,"
Word Ways: Vol. 40
, Article 7.
Available at: http://digitalcommons.butler.edu/wordways/vol40/iss3/7