The Social Security number is composed of a 3 digit area number, a 2 digit group number and a 4 digit serial number; a serial number is a unique number.
The total Social Security numbers that can exist is based on the number of area numbers, group numbers and serial numbers possible.
The 10 digits used for a Social Security number are 0,1,2,3,4,5,6,7,8,9.
How many area numbers, group numbers and serial numbers are possible? We use math to find the answer.
Please refer to another article on this site for the details of how each group of numbers is determined for a phone number;
the mehtod is the same for the social security number.
Why Does My Telephone Area Code Have To Change!
Using the methods of math we can have 10 X 10 X 10 or 1,000 possible 3 digit area numbers, 10 X 10 or 100 possible 2 digit group numbers,
and 10 X 10 X 10 X 10 or 10,000 possible 4 digit serial numbers.
Due to Social Security Administration regulations certain numbers within each category are not currently available to use:
* area numbers between 734 and 749, or above 772
* numbers with all zeros in any digit group
* area number 666
* numbers from 987654320 to 987654329 are reserved for use in advertisements
Area numbers not available are:
734  749 for a total of 16
772  1000 for a total of 229
000 for a total of 1
666 for a total of 1
The total number of area numbers not available is 247.
The total of 1,000 possible 3 digit area numbers is reduced by 247 to 753.
Group numbers not available are:
00 for a total of 1
The total number of group numbers not available is 1.
The total of 100 possible 2 digit group numbers is reduced by 1 to 99.
Serial numbers not available are:
0000 for a total of 1
The total number of serial numbers not available is 1.
The total of 10,000 possible 4 digit serial numbers is reduced by 1 to 9,999.
In summary, there are 753 possible 3 digit area numbers each of which can have 99 possible 2 digit group numbers and each of
these can have 9,999 possible 4 digit serial numbers. So 99 group numbers X 9,999 serial numbers = 989,901 possible numbers for
each possible area number; then 989,901 X 753 area numbers = 745,395,453 possible social security numbers. We then have to reduce this total by numbers
from 987654320 to 987654329 or 10, so 745,395,453  10 = 745,395,443 possible social security numbers currently available.
As the population of the US increases, the demand for social secutiy numbers grows and the currently not available area numbers will have
to made available for use.
*Note: If we were able to utilize 245 of the currently unavailable area numbers that are classified as not ready to issue,
we would have 753 + 245 = 998 possible 3 digit area numbers.
Then the 989,901 possible numbers for each possible area number X 998 area numbers = 987,921,198 possible social security numbers;
there is room for almost a billion social security numbers.
The source for this article is:
Wikipedia  Social Security number
