Hick's law is used.

Schick's law is also called restraint's law. The bank card number is entered every 4 digits. The purpose is to reduce the memory cost and improve the readability of the information, so as to achieve the role of visual error prevention.

The number of digits in different bank cards is different, and it is related to the type of card and the bank unit to which it belongs. The number of digits in bank cards can be divided into two categories: 1. Debit cards are usually called savings cards, and the card number is usually 19 digits. There are also special circumstances, such as China Merchants Bank, Construction Bank 16th, Bank of Communications 17th, etc. 2. Credit cards are usually referred to as credit cards. The unified card number of all banks is 16 digits. Examples of common digits in various banks: 1. China Construction Bank: 16 or 19 digits for debit card numbers, 16 digits for credit cards 2. Agricultural Bank of China: 19 digits for debit card numbers, 16 digits for credit cards 3. ICBC: 19 digits for debit card numbers, 16 digits for credit cards 4 , Transportation: Deposit card number is 17 digits, credit card number is 16 digits 6. People's livelihood: Deposit card number is 16 digits, credit card number is 16 digits.