The bank account number at the beginning of SN means SerialNumber, and sn is the English abbreviation of serial number, and the full name is serial number. The serial numbers of bank cards range from 16 to 19 digits, with 19 digits for the four major state-owned banks and 16 digits for some joint-stock commercial banks.

Bank card refers to a credit payment tool issued by commercial banks (including postal financial institutions) with all or part of the functions of consumer credit, transfer settlement, cash deposit and withdrawal, etc. Bank card reduces the circulation of cash and checks, which makes the banking business break through the limitation of time and space and undergo fundamental changes. The application of bank card automatic settlement system makes the dream of "no cheque, no cash society" come true.