510 books • 53 series
Hard Puzzles Book - Suguru, Binary, Tapa, Straights - 200 Hard Puzzles vol.10 (Hard Puzzles Book, #10)
Hard Puzzles Book - Slitherlink, Hashi, Futoshiki, Numbricks - 200 Hard Puzzles vol.9 (Hard Puzzles Book, #9)
Hard Puzzles Book - Jigsaw Sudoku, Non-Consecutive Sudoku, Kropki Sudoku, Chain Sudoku - 200 Hard Puzzles vol.8 (Hard Puzzles Book, #8)