The book of the wonderful popularizer of science Yakov Isidorovich Perelman "Entertaining arithmetic. Riddles and curiosities in the world of numbers" - the next issue of the series "Entertaining Science," published by our publishing house. The first edition of Entertaining Arithmetic 1 was published in 1926 by the Leningrad publishing house Vremya. Like other books by Y. I. Perelman, this book immediately fell in love with readers and withstood seven editions during his lifetime and several editions after his untimely death in besieged Leningrad. The ninth edition was published in the Moscow publishing house Fizmatgiz in 1959 with additions by A. 3. Ryvkina.