The major credit card associated with account numbers that universally start with the digit 5 is Mastercard.
This is due to a system known as the Major Industry Identifier (MII), where the first digit of a payment card number signifies the network or industry that issued it. For Mastercard, the MII is specifically designated as 5 (ranging from 51 to 55), meaning all primary account numbers (PANs) for cards processed on their global network will begin with this digit. This designation is essential for payment systems to instantly route transactions to the correct authorization network.
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