Pi number is perhaps the most surprising and paradoxical in the world of mathematics. Despite the fact that many books are devoted to it, it is rightfully considered the most studied and it is quite difficult to say something new about it, it still attracts the inquisitive minds of researchers. For people far from mathematics, pi is surrounded by many mysteries. Do you know what scientists think pi decimals are for? Why do we need a list of the first billion characters I? Is it true that science knows everything about pi and its signs? This book will help you find the answer to these and many other questions.