14 books • 6 series
Book #1: Easy Difficulty Sudoku Puzzles Volume 1
Book #1: Hard Difficulty Sudoku Puzzles Volume 1
Book #2: Hard Difficulty Sudoku Puzzles Volume 2
Book #1: Medium Difficulty Sudoku Puzzles Volume 1
Book #2: Medium Difficulty Sudoku Puzzles Volume 2
Book #1: Random Easy To Very Hard Sudoku Puzzles
Book #1: Very Hard Sudoku Puzzles
Book #1: Very Hard Sudoku Puzzles Volume 1
Book #2: Very Hard Sudoku Puzzles Volume 2