j-1064772 (5/4/2016)

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For "older" social security numbers, the range is LESS than the theoretical 1 billion numbers.

According to Wikipedia, the US Social Security Number does NOT include a check digit dependent upon the preceding digits. (Canada does, so its 9-digit format yields a number range of 8 digits plus a modulo 10 calculated digit).

However, some US numbers are not allowed:

-Numbers with all zeros in any digit group (000-##-####, ###-00-####, ###-##-0000)

-Numbers with 666 or 900-999 (Individual Taxpayer Identification Number) in the first digit group

Before full randomization starting June 25, 2011, the number assignation process was based on a pattern involving the area (AAA) and "group" (GG) followed by a4-digit serial number (AAA-GG-SSSS).