[T-A]

> a national ID number isnt usually publicly available info

A couple of counterexamples:

Italy's "fiscal code" is generated with a simple algorithm which can be executed manually:

https://en.wikipedia.org/wiki/Italian_fiscal_code

Sweden's "personal identity number" is public information and can be looked up by anyone:

https://en.wikipedia.org/wiki/Personal_identity_number_(Swed...

[sam_lowry_]

Belgian National Number is your birth date, then an increment from 1 to 999 for every baby born that day, then a base-97 checksum.

[andruby]

Not sure if still the case: odd numbers for males and even numbers for females.

This also means a person’s Belgian RRN can change.

[sam_lowry_]

Yep, but they do not change on sex change, IIRC.

[andruby]

I wrote a system for a medical lab decades ago and IIRC I did actually have to change some RRN's manually. It's been a while so I'm not 100% sure, but I do think the changes were due to switching gender.

[port11]

Are there never more than 1k babies born in a day?

[treszkai]

With a population of 12M and life expectancy of 80 years (give or take), probably not, as that needs ~400 newborns a day to maintain, and the birth rate is probably well below that, like in most Western countries.

[port11]

Back-of-the-napkin math supports that, but baby births aren’t uniformly distributed. Well, anyway, I’m sure they thought about it. Thanks for explaining how I got my Belgian ID number!

[sam_lowry_]

For the curious, there is a lot more about National Numbers in this pdf: https://www.ibz.rrn.fgov.be/sites/default/files/documents/nl...