Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In number theory, a prime number is called weakly prime if it becomes composite when any one of its digits is changed to every single other digit.[1] Decimal digits are usually assumed.Number theory is the branch of pure mathematics concerned with the properties of numbers in general, and integers in particular, as well as the wider classes of problems that arise from their study.Number theory may be subdivided into several fields, according to the methods used and the type of questions investigated. (See the list of number theory topics.)