The last digit may be a check digit. In particular, it might be the remainder upon dividing the number that the other digits make by 7. For example 82777850 d

The last digit may be a check digit. In particular, it might be the remainder upon dividing the number that the other digits make by 7. For example 82777850 divided by 7 leaves a remainder of 1. Some examples of this check digit scheme: http://nrich.maths.org/2036 http://nrich.maths.org/2036 http://www.cbp.gov/sites/default/files/documents/in_bond_check_1.pdf http://www.cbp.gov/sites/default/files/documents/in_bond_che... (with a clunky implementation) http://www.con-way.com/en/tools_pricing/freight/fr_tools/tracking/pro_number_check_digit_formula http://www.con-way.com/en/tools_pricing/freight/fr_tools/tra...