I don’t know mine. I have to look at my card whenever I purchase something online. Why? It seems to me that I type or say my credit card number as much as I type or say my phone number, and I would consider it totally weird not to have my own phone number committed to memory.
On the other hand, my youth was spent in an environment where you had to recall your own phone number all the time, because it wasn’t programmed into your phone and you had to dial it every time you wanted to use it. So the followup question for those readers who grew up in the cellphone era is: do you know your own phone number by heart?