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 (R) Calendars are environmentally friendly! Printed on responsibly sourced paper and 100% recyclable, with sturdy cardboard backers.