 Computer programs are often used to "search" for Sudokus with certain properties, such as a small number of clues, or certain types of symmetry.Over 49,000 Sudokus with 17 clues have been found, but discovering new distinct ones (not transformations of existing known Sudokus) is becoming more difficult as undiscovered ones become more rare.One common method of searching for Sudokus with a particular characteristic is called "neighbor searching".