The number assigned by the Patent Office when a patent application is submitted. It is not the number that is assigned to a patent itself. In the US, the application number is a 2-digit series number followed by a slash and then a 6-digit serial number. (Example: 10/007521). For EP patents the application number is an 11-digit number where the first 4 digits indicate the filing year of the application. (Example: EP20010402190).