in reply to Testing numeric strings

What it seems like you need is a universally unique identifier (UUID). If you are using MySQL you can use UUID() (see http://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_uuid).

Other databases generally provide a similar function. These are pretty much always unique numbers. They are not unpredictable but that didn't seem to be a requirement.