the current 16-digit credit card number is stipulated by international standards. Generally, the first six digits are BIN, which is allocated by international card organizations. The first digit of a credit card number is 4, and 5 is Master. 622126~622925 are UnionPay standard cards. 6 starts with China UnionPay single currency card (or American discover), credit card number 4 starts with international brand VISA credit card (the world's first credit card organization), 5 starts with international brand MASTERCARD, and 3 starts with Japanese JCB and AMERICAN EXPRESS. The 7th-15th rows are allocated according to their own needs, and the 16th is the parity bit. Other non-16-digit card numbers are assigned by banks themselves.