Below are some common conceptual examples and explanations that are publicly available. However, please note that the specific generation rules of passport numbers are internal management information of government agencies of various countries, and many details (including whether to use a checksum algorithm, serial number allocation method, etc.) are not made public. The following content is only an overview of common practices in various countries and does not constitute any guidance for illegal use: ────────────────────────── 【1. Different rules in different countries】 • Passport numbers in different countries usually use letters, numbers, or a combination of the two to distinguish the type of passport, issuing region, version, etc. • Some countries may embed a "check digit" in the number to reduce data entry errors, but the algorithm is often not public or is limited to internal verification. • Numbering rules often take into account both anti-counterfeiting needs and the system's efficient allocation and management of numbers. ──────────────────────── 【2. Common examples (for illustration only, not representing the actual generation algorithm)】 (a) US passport: – Form: Traditionally, US passport numbers are mostly 9 digits (for example: 123456789). – Note: The specific allocation method of US passport numbers and whether an internal verification mechanism is used are not fully disclosed. The number generally looks like a string of seemingly random numbers, but in fact it may be the result of internal random or batch allocation. (b) Ordinary passports of mainland China: – Form: The common format starts with a letter followed by a number of numbers, such as "G12345678" or "E12345678". – Note: Letters are usually used to indicate the type of passport or issuing agency (for example, "G" is often used to indicate ordinary citizen passports, while sometimes other letters may be used for diplomatic passports); the subsequent numbers may be related to the order of application, issuance time, etc., but the specific allocation algorithm is an internal management content and is not disclosed to the public to prevent the risk of counterfeiting. (c) Passports of some European countries: – Form: Some countries may use a mixed number and letter method, such as "C01X9Y2Z3". – Note: The letters and numbers in these numbers may represent region codes, issuance years, or even internal security identification, but in general, the specific rules of each country are different, and many details are confidential. ────────────────────────── 【3. Considerations behind the generation rules】 • Anti-counterfeiting design: As part of an official identity document, the passport number is often designed to prevent forgery and incorrect input, so a check digit may be built into the number or a specific distribution rule may be used. • Database management: Passport numbers usually need to be associated with other information of the applicant. The design must avoid duplication and facilitate query management. • Security and confidentiality: For national security and to prevent document forgery, many countries will not disclose all generation algorithms, but only the number format ("a structure that looks like..."). ────────────────────────── 【Important statement】 The examples and explanations described above are only to introduce the "format logic" and concepts roughly used by various countries, and do not represent the actual complete generation algorithm of any country. In addition, it is illegal to use such information for forgery or illegal purposes. This answer is only for understanding and popular science purposes. I hope everyone respects the laws and regulatory provisions of various countries. In summary, each country has its own specific rules for generating passport numbers. The basic ideas include distinguishing passport types, adding anti-counterfeiting checks and ensuring uniqueness. However, the specific algorithms and internal details are generally not disclosed. Therefore, what is seen in public channels are mostly format examples rather than complete generation mechanisms.