Chile
In Chile the National Identification Number is called RUN (Rol Único Nacional); but is usually called RUT (Rol Único Tributario) and the number is the same. The difference between them is that RUT is also used for juristic persons.
It is used as a national identification number, tax payer number, social insurance number, passport number, driver's license number, for employment, etc. It is also commonly used as a customer number in banks, retailers, insurance companies, airlines, etc.
Since well before 1990, every baby born is given a RUN number; previously it was assigned at the moment of applying to get the ID card. Non-Chilean residents also get a RUN and an identification card.
Every company or organization also must have a RUT for taxation purposes.
The RUN or RUT has 7 or 8 digits (for people alive today; in the past, there were persons with a 5- or 6- digit one, but have died off) plus a check digit or letter (xx.xxx.xxx-z, z is {0-9, K}).
Code (C#) for checking correctness of RUT can be found on the here: http://www.vesic.org/english/blog/c-sharp/verifying-chilean-rut-code-tax-number/
Read more about this topic: National Identification Number