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Comment by jgrahamc | Hacker News Reader

All the card numbers start 5424 (Citibank MasterCard) and there are actually only a small number of different card numbers.

I wonder if this is something to do with test data.

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Anyway what were they testing? The "publish_credit_card_numbers" module?

5424 is a MasterCard test number. http://www.topbits.com/test-credit-card-numbers.html

edit: I was wrong, it's the full number that's a test number. 5424 0000 0000 0015

So you're telling me that I've been using a test card for the past 5 years? I hope not.

The two numbers listed on that site are test numbers. 5424 is a very common MasterCard prefix.

I'm reasonably sure that's not true. Perhaps the whole 16 digit sequences listed there is a test number.

You are right, I was wrong. It's the full number that's a test number. 5424 0000 0000 0015

There are the only 4 numbers in the results. Although I do see a few in this format XXXXXXXXXXXX2376.

(Edited to remove actual numbers in case they're not test numbers)

My actual MasterCard # starts with 5424.

According to the link that you posted, 5424 0000 0000 0015 is a test number. That's not the same number that I'm seeing in the Google results.

5424 is also used outside of Citibank as my old debit card (with a MasterCard logo) from Fifth Third Bank started with 5424. I don't believe they're affiliated with Citibank, but I could be mistaken.

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