I’m insulted they thought I didn’t know what a LUHN check is.

Of course, my current credit cards don’t even have a magnetic stripe, so the original purpose for the check digits is history. Still useful for ither situations where the number might get garbled though.

The other thing useful about credit cards is that the first set of digits refer to the issuer, not your account. Once you strip off the issuer code and the check digit, there’s much less that’s unique to your card.