393153 random code/number

I've developed a website that offers an internet certificate to potential customers. They are encouraged to print the certificate and bring with them in person to honor either a $10 off discount or an item. I've found that some prospects can't print because they don't have a printer. I would like the printable coupon to generate a random number (numeric or alphanumeric), and have this code/number emailed to me and viewable to the customer for verification upon request of offer.