we turn coffee into puzzles

Puzzles for Taking Sudoku Seriously These nine puzzles appeared in the article Taking Sudoku Seriously, Laura Taalman, Math Horizons, September 2007.

Minimum Sudoku The numbers 1--9 must each appear exactly once in each row, column, and block. This is an example of an 18-clue puzzle! 18 clues is the minimum known number of clues in a symmetric Sudoku puzzle that will determine a unique solution.

Sudoku Brothers For each puzzle, the numbers 1--9 must each appear exactly once in each row, column, and block. What is interesting here is that both of these puzzles have the same solution. (Obviously you shouldn't look at one while you play the other, or you'll have additional information!)

Snowflake The numbers 1--9 must each appear exactly once in each row, column, and block, and no numbers are repeated in any marked diagonal.

Pyramids The numbers 1--9 must each appear exactly once in each row, column, block, and pyramid.

Jigsaw The numbers 1--9 must each appear exactly once in each row, column, block, and jigsaw region.

Rainbow Wrap Up The numbers 1--9 must each appear exactly once in each row, column, block, and colored region. Notice that the colored regions wrap around the board; for example, the green region consists of all nine of the green cells in the puzzle.

Worms The numbers 1--9 must each appear exactly once in each row, column, and block. In addition, each worm should consist of an increasing sequence of numbers from tail to head. For example, a worm of length four could contain the numbers 2, 5, 6, and 8, in that order from tail to head. You have to figure out the direction of each worm.

Mystery Sums The numbers 1--9 must each appear exactly once in each row, column, and block. In addition, all shaded regions of a given color add to the same sum; for example, if one red shaded region has entries that sum to 21, then all red shaded regions in that puzzle sum to 21. The sums are not given; you must determine them yourself.