algorithms are a bad thing
Acompany I worked at used to derive the employees ID based on surname, birthdate and SSN.
Know one of the latter two and you could - if you knew the algorithm - work out the other.
One colleague spent many a happy moment surprising others with their SSN once he'd figured out their birthday.
And since many of the applications we used asked for one or both as authenticationat initial login......
Probably why they switched to a random one letter - 6 digit number combo :-)