Some computer software contain social security number (sofi nummer) checks for making sure that the user fills in the correct social security number. The social security number can be tested by a similar 11-digit-check, which is used a lot for testing electronic payment transfers (on 9 and 10 digit bank account numbers), to check if they are valid.

The 11-digit-check multiplies every number with it’s position, adds these numbers up and divides the result by 11. The result should be > 0.

For example, bank account number: 73.61.60.221 can be calculated:

   (7 ×9 + 3 ×8 + 6 ×7 + 1 ×6 + 6 ×5 + 0 ×4 + 2 ×3 + 2 ×2 + 1 ×1) / 11 = 16

For social security numbers the formula is a bit different.
The last number will be multiplied by position -1 instead of 1.

Now of course tools like this do already exist:
Check the following URL:
http://www.wilmans.com/sofinummer/index.html