I'm not a serious stamp collector, but I found these on the Internet.

"The Presidential Issue, nicknamed the Prexies by collectors, is the series of definitive postage
stamps issued in the United States in 1938, featuring all 29 U.S. presidents who were in office
between 1789 and 1928, from George Washington to Calvin Coolidge. The presidents appear as small
profile busts printed in solid-color designs through 50¢, and then as black on white images
surrounded by colored lettering and ornamentation for $1, $2, and $5 values." – Wikipedia