A car's 17-digit VIN has a similar feature, for model years since 1981.
The 9th digit is the check digit, and it's a much more complex algorithm (since the VIN can have numbers and letters.)
this post was submitted on 12 Aug 2025
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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 other 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.
The check digit is to catch a mistyped number.
That's pretty neat. I was expecting something basic like "pay it off every month and there's no interest", but this was much more interesting.
It's a method that web pages use to make sure you didn't make a typo in the number.
Presumptuous, smug, know it all, clickbait titles still didn't die?
Fuck me, if I were in America and had to read toss like that, I'd probably think the population of 'scientific' americans contains a larger than normal proportion of cunts.
It’s a similar idea to how some RAID configurations work.