This book tells about one little-known area of ​ ​ Karl Marx's scientific interests - about his studies in mathematics. The problems that worried him in this science are by no means easy to understand. Nevertheless, no matter how far the reader is from the exact sciences, he has no reason to be afraid of the "abyss of wisdom" unfolding in front of him. After all, we will not talk about mathematics itself, but about what fascinated Marx in it. Marx, who cared about the very foundations of any problem - so general and deep that they are of interest to everyone who is used to thinking. Marx, who illuminated any business with the light of his genius.