Passport number is an important information used to uniquely identify the holder. The generation rules and formats of passport numbers vary from country to country, and are usually composed of a combination of letters and numbers. The following are examples of passport numbers of some countries and their generation rules: ### 1. **US Passport Number** - **Format**: 9 digits - **Example**: `123456789` - **Description**: US passport numbers are usually composed of nine pure digits without letters. Each number is unique and is used to distinguish different passport holders. ### 2. **Chinese Passport Number** - **Format**: Starts with the letter "G" or "E", followed by 8 digits - **Example**: `E12345678` - **Description**: - "G" represents an ordinary passport (Diplomatic or Official passports start with other letters, such as "D" or "O"). - The number part is a unique identification number, which is randomly generated when each passport is issued. ### 3. **UK Passport Number** - **Format**: 2 letters + 6 numbers + 1 letter - **Example**: `AB123456C` - **Description**: - The first two letters are the letter prefix, which is used to identify the passport type. - The six digits in the middle are the unique identification number. - The last letter is the check digit, which is used to verify the validity of the number. ### 4. **Canadian Passport Number** - **Format**: Letters + 7 digits - **Example**: `A1234567` - **Description**: - The first letter is usually a letter, followed by seven digits. - Each number is uniquely assigned and used to identify the holder. ### 5. **Australian Passport Number** - **Format**: 1 letter + 7 numbers - **Example**: `N1234567` - **Description**: - The first letter indicates the passport type. - The following seven digits are the unique identification number. ### **General description of generation rules** 1. **Uniqueness**: Passport numbers must be unique within the same country to avoid identity confusion. 2. **Character type**: Most countries' passport numbers are a combination of letters and numbers, and some countries may use pure numbers or specific letters at the beginning. 3. **Length**: The length of passport numbers varies from country to country, usually between 8 and 9 digits. 4. **Verification mechanism**: Some countries add verification codes or use specific algorithms in passport numbers to ensure the validity of the number and prevent incorrect input. ### **Notes** - **Privacy protection**: Passport numbers are personal sensitive information and should be kept properly to avoid disclosure. - **Risk of counterfeiting**: Understanding the generation rules of passport numbers can help identify potential counterfeit numbers, but it is not recommended to try to generate or use unofficial passport numbers. In short, the design of passport numbers is to ensure that each holder has a unique and difficult-to-counterfeit identifier. The specific generation rules and formats vary from country to country and are usually formulated by relevant government departments based on security and management needs.