P Van D, Yes, I read about the design competition in an article on wikipedia, here is the link, if you haven't read it already: https://en.wikipedia.org/wiki/Presidential_Issue
It is interesting how they numbered the stamps to correspond to postal needs and the order of accession. It was complicated, but they made it work as well as possible, though some of the stamps never met a true postal rate need. They also made concessions for the non-presidents and irregular postage rates, by assigning the rates to Martha Washington, Ben Franklin, etc., and, of course, they had to break off the numerical list of presidents by accession and start the higher values at Teddy Roosevelt 30 cents, when he was actually the 26th President, etc. It's all in the wiki article. It is interesting to me, because I never really realized that all of this was planned this way for this issue. I don't have all of the Prexies on cover. They can be hard to find and costly, but one of my favorites is my small invitation size envelope, including the invitation, with the 1 1/2 cent Martha Washington, to meet the rate for that type of mailing during that period of postal history, that I found in a dealers box at a local stamp shop probably 30 years ago, before it closed about 10 years ago. I miss going there, buying my Linn's weekly stamp news, having a cup of coffee from the dime a cup pot, looking at stamps and covers, and buying what I needed for my collections and visiting with Dick, the owner. Good times, never forgotten.
I am surprised that Mr. Adams never made it to banknote status, either, nor to a coin, except, I think for the presidential dollar series or something. I am not much of a numismatist. The constitution is a very interesting part of our history and government and I am always amazed at what I don't know about it and the stories that I read about how it was formed and has impacted all of our lives, for the better, after all of these years.
I didn't realize that John Q. Adams, his son, was on or considered for currency. What and when was that?
Thanks again for bringing up the John Adams Prexie issue and for this great discussion. I have enjoyed it, as well. Be well and enjoy the rest of your weekend. :-)