You have decided to teach mathematics - whether in elementary school, middle school, or high school? In this book, you will explore the world of natural numbers and their diverse patterns and structures. And you will do so in a way that you would also wish for your students to engage with mathematics. You won't just learn dry facts; instead, you will be invited on a mathematical journey of discovery. Through many interesting problems, you will be encouraged to independently explore numbers and their structures. In easily accessible and entertaining texts, you can then reflect on your experiences and build a solid and systematic understanding of the fundamentals of arithmetic. If you want to deepen your knowledge, a variety of practice exercises are available, allowing you to not only review the content.