Mathematical divertissement

The proposed book contains thirty lectures on various stories from algebra, combinatorics, geometry and topology, both classic and modern. Lectures are independent of each other, and they can be read in any order. A few cross links are designed only to demonstrate the connection between different subjects.
The volume of alleged knowledge varies from a lecture to a lecture, but never significantly goes beyond the scope of the school program. A significant part of the material under discussion is not contained in standard textbooks, but nevertheless, it includes at least the knowledge necessary for each mathematics. Almost every lecture contains mathematical surprises even for experienced researchers. Almost all lectures contain problems, the solutions of some problems are given at the end of the book. The mathematical beauty and grace are united for the presentation of the topic: the unity of mathematics is the leitmotif of the book.
The book is richly illustrated: it has more than 400 drawings, about 40 illustrations and 90 portraits of mathematicians, the results of which are discussed