National registry number

Solution

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In Belgium every citizen has a National registry number, which is created by using the citizen's date of birth (encoded in six digits), followed by a serial number (three digits) and a checksum (two digits). The serial number is used so that men get the odd numbers, while women get the even numbers (thus, there can be only 500 men or women per day).

Messages

Tip

Try the numbers 64101612335 (correct), 6410161233 (not 11 digits) and 64101612330 (one faulty digit)