The Inverted Jenny was discovered by Willian T. Robey on May 13, 1918. Its denomination is 24 cents. The stamp was produced three days before its discovery. It was originally purchased as a sheet, but was broken up into 50 pieces in order to be sold to collectors. One block of four Inverted Jennies was sold for more than 2 million dollars. There are about 100 Inverted Jennies in existence. One was sold for $977,500.