This book is AWESOME! Anyone above first grade NEEDS this in their collection. It is full of picture puzzles. Each prime number is represented by a monster and either a monster or group of monsters is used to represent the numbers 1-100. Excellent visual representations for factor trees. Now I need to figure out the best way to use it with my littles. If anyone out there is using it with their 6 and 7 year olds, please share what you're doing!