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.

Used too, But anyone under the age of 20 will have a random SSN [1]

1: https://www.ssa.gov/kc/SSAFactSheet--IssuingSSNs.pdf

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 presume there are a lot of non-Americans with SSNs: I have one from working in the US on a working visa.