The collection "Entertaining Mathematics" is based on the second supplemented edition of Y. I. Perelman's book "Entertaining Mathematics," published by the Leningrad publishing house "Vremya" in 1928 and two rarely published popular science essays commenting on science fiction works - "Upside Down" by J. Verne and "Scooter railway between St. Petersburg and Moscow" A. A. Rodnykh, published by Perelman in other publications of those years