your idea plz: customer account number

[C# Programming]

can you please tell me your idea plz..

I want to create an accoutn number for every customer when they entered his details in my C# application..

and of course it must be unqiue account number

I though of the following:

DayOfYear + Month + Day + DayOfWeek + the_primary_key_from_customer_table

any other better idea?