There are two different options you can use, that is: GJ99-VX9Z-P4WC-FP4U-GRLD or DF66-3M6M-UC59-6UC3-DRLD . However, the best means to get your Sims 3 serial number is to use a product key finder program. You can also find more from this link https://www.thesims3.com/register.html.
please help help ! I just tried to install sims 3, and I used registration code, that you suggested but later the program ask me to re-enter that registration code, but it wasn't work. What should I need to do ? Please give me an answer