4 ms·

Five cards per person is less than a billion cards, vs a quadrillion possible combinations of 15 digits. A drop in the bucket

• henearkr 6y ago
  You forgot that these 16 digits have a structure, with the 4 or even 8 first ones being determined by the type (visa, mastercard) and the bank/country, etc.
  • nikanj 6y ago
    That's a made-up problem, and the right solution is not adding more digits to the cards.