"X" is a letter of the alphabet. All serial numbers on notes these days begin and end with a letter of the alphabet. What exactly about this troubles you?
In older notes they had a change in the paper once They had three different % in the paper of rag to pulp. They had "X", "Y", "Z" in the last letter as to the %. I think they were the "Silver Cert".
Typically, the San Francisco district (prefix L) has the most notes printed in any particular series and denomination. Followed by Atlanta (F) and New York (B) which uses most of the alphabet suffixes.
Serial numbers start at 00000001 and end at 96000000 (actually, I believe it’s 95999999 and a star note is used for 96000000). For each federal reserve district starts at 00000001A. When they run out of numbers the begin again at 00000001B and so on. Your series 2009 note is from the San Francisco Fed district. They printed so many $1 notes that they made to X. That’s 1-9600000 twenty-three times (They don’t use the letter O). BTW: Worth $1
Not sure what you're finding special. They are from two different series 2006 & 2017. Again, please point out what you see as special. All the notes you posted I see as spenders. YMMV
Go find me a any denomination U.S dollar with a repeating serial number (((OR))) a U.S dollar with the letter ‘X’ at the end of the serial number (((OR))) - Edited - please and thank you
All in my possession: FYI, my FRN's don't have much premium value if any. I don't see yours being even as desirable as mine. and you're welcome.
@Kein This is an old thread. You will receive much better answers if you started a new thread. Post pictures as well if you have them. I will tell you from your description it sounds as if all you have are normal bills.