This book is not a systematic course in "entertaining mathematics." Her goal is completely different. Reading about interesting and useful things that the book tells about, the reader will be able to have an exciting time, will be able to have a good rest after work. The stories of which it consists are very short, but they touch on questions that will undoubtedly interest every inquisitive reader. More difficult topics are interspersed in the book with hilarious stories, aphorisms and puzzles, and short stories from the history of mathematics and related sciences.