Sudoku is the latest craze in puzzles, and is played by entering digits from 1 to 9 to complete a partially filled 9x9 grid so that each digit appears exactly once in each row, column, and 3x3 subgrid. While no math is required to play the game, a branch of mathematics called combinatorics is a useful tool for studying many aspects of the game and its variations. Combinatorics is the study of discrete patterns or combinatorial objects, often to count them or find relationships between the objects.

A Sudoku game grid is a special case of a combinatorial object called a Latin square, an nxn grid where each digit from 1 to n appears exactly once in each row and each column. Latin squares have been studied extensively, but the mathematics of Sudoku is a relatively new area of combinatorial research, and as such has the advantage of many opportunities for exploration and original results. In fact, very few results about Sudoku have been published, and most conjectures are related to only the standard form of the Sudoku game.

There are numerous variations of the familiar Sukoku game that are also based on Latin squares, but have different additional requirements instead of the subgrids. These variations make Sudoku a particularly rich topic for a variety of investigations, including mathematical topics such as equivalence relations, inclusion-exclusion, and partially ordered sets.

The article Taking Sudoku Seriously, written by Dr. Laura Taalman, was published in the September 2007 Math Horizons magazine. It has a very accessible introduction to some possible research questions and variations of Sudoku.

# Summer 2015 REU

## What will the project involve?

We will use techniques from discrete mathematics to analyze one or more Sudoku variations. This analysis will include topics such as puzzle solving techniques, determining when a Sudoku board is solvable, counting the number of possible Sudoku puzzles, and generating valid puzzles.

## Desirable experiences for applicants:

Applicants should have some experience in topics in discrete mathematics including combinations, permutations, and inclusion-exclusion counting techniques. Some programming experience is recommended but not required. Applicants should also enjoy solving puzzles, be able to work independently as well as in a team, and be interested in improving their mathematical writing and presentation skills.