Saw this FOX Business article about two orders of dollar bills from the Fed mistakenly printed with identical serial numbers, meaning each bill from the first order has a 'twin' in circulation from the second order. The article says there were 6 million of these bills printed, and if you can somehow find two with identical numbers, you're sitting on money worth way more than $2. Of course, the odds of ending up with two bucks with the same serial number are probably lower than being struck by lightning while doing a handstand, but some matches have been made, and they've sold for as much as $6K. Somebody created a website where you can enter the serial numbers of your dollars and if your 'dollar twin' has been entered into the system, it'll connect you. I can't imagine doing this with every dollar I come across, but I'm going to try it with a few. Why not? 

https://project2013b.blogspot.com/2021/10/welcome.html?m=1

ttps://www.foxbusiness.com/lifestyle/rare-1-bills-printing-error-could-worth-thousands-still-out-there