The Brazilian CPF (our equivalent to the SSN) goes up to eleven (literally) by including not one, but two check digits; IIRC, the first one (the tenth digit) is

The Brazilian CPF (our equivalent to the SSN) goes up to eleven (literally) by including not one, but two check digits; IIRC, the first one (the tenth digit) is computed over the first nine digits, and the second one (the eleventh digit) is computed over the first ten digits.