22 books • 6 series
Book #1: Christmas Sudoku
Book #1: The Ugly Christmas Sweater Sudoku
Book #2: Santa Sudoku
Book #3: Christmas Sudoku S*cks!
Book #1: Extreme Sudoku
Book #1: Easy Sudoku Puzzle Book
Book #2: Medium Sudoku Puzzle Book
Book #3: Hard Sudoku Puzzle Book
Book #4: Expert Sudoku Puzzle Book
Book #5: Extreme Sudoku Puzzle Book