76 books • 2 series
Sudoku Book 1,000 Puzzles, 500 Medium and 500 Hard (Sudoku Book, #6)
Sudoku Book 1,000 Puzzles, 500 Hard and 500 Extra Hard (Sudoku Book, #7)
Sudoku Book 1,000 Extra Hard Puzzles (Sudoku Book, #4)
Sudoku Book 1,000 Easy Puzzles