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Before 1986, people often did not obtain a Social Security number until the age of about 14, since the numbers were used for income tracking purposes, and those under that age seldom had substantial income.
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The Social Security number is a nine-digit number in the format "AAA-GG-SSSS". <21> The number is divided into three parts.
The Area Number, the first three digits, is assigned by the geographical region. Prior to 1973, cards were issued in local Social Security offices around the country and the Area Number represented the office code in which the card was issued. This did not necessarily have to be in the area where the applicant lived, since a person could apply for their card in any Social Security office. Since 1973, when SSA began assigning SSNs and issuing cards centrally from Baltimore, the area number assigned has been based on the ZIP code in the mailing address provided on the application for the original Social Security card. The applicant's mailing address does not have to be the same as their place of residence. Thus, the Area Number does not necessarily represent the State of residence of the applicant, neither prior to 1973, nor since.
Generally, numbers were assigned beginning in the northeast and moving south and westward, so that people on the east coast had the lowest numbers and those on the west coast had the highest numbers. As the areas assigned to a locality are exhausted, new areas from the pool are assigned, so some states have non contiguous groups of numbers.
So, Obama graduated from high school in 1979 in Hawaii and immediately went to college in California, a state with a rapidly growing population at the time and that, IMO, was likely to have lots of non contiguous Area Numbers. So, if he got his SSN while going to college (a reasonable assumption, right?), then it could easily be something "unusual".