In the United States, The Social Security number (SSN) is a nine-digit number issued to U.S. temporary (working) residents, permanent residents, and citizens. It is issued to an individual by the Social Security Administration. Now, The SSN has become a de facto national identification number for taxation and other purposes
The Social Security number is divided into three parts in the format "AAA-GG-SSSS". the first three digits, is assigned by geographical region. The middle two digits are the Group Number. The last four digits are Serial Numbers represent a straight numerical sequence of digits from 0001 to 9999.