My understanding is that a portion of the SSN is based on the ZIP of your birthplace. I'm sure some clever person could come up with a way to use birth location + a checksum that would reveal an SSN without actually typing it out.
I'm thinking something like, "Add up all the individual numbers of your SSN and figure out what Founding Father you are!" Use some statistics to ensure that lots of people get good ones.
The first 5 digits are directly correlated to DOB and birthplace, the last 4 are mostly random.
https://www.pnas.org/content/106/27/10975
There's a pretty interesting study done on this.
I'm thinking something like, "Add up all the individual numbers of your SSN and figure out what Founding Father you are!" Use some statistics to ensure that lots of people get good ones.