A year of Sudoku puzzles hand-crafted by Nikoli, the Japanese company that invented the game. THE BEST SUDOKU: Every puzzle in this calendar is created by Nikoli, the best Sudoku makers in the world not a computer to balance toughness and solvability and keep you hooked. TRAIN YOUR BRAIN: The week begins with the easiest puzzles and the difficulty increases day by day. Just in case you need them, solutions are printed on the back of the pages. NOW PLASTIC-FREE!: Page-A-Day Calendars are environmentally friendly! Printed on responsibly sourced paper and 100% recyclable, with sturdy cardboard backers.