A** sequence** is a string of numbers (called terms) that follow a specific pattern. The terms in a sequence are numbered (meaning there is a first term, a second term, and so on) and are generally described with the notation a_{n} where *n* is the number of the term.

In an** arithmetic sequence**, the difference between each term is the same (a value called the **common difference**). For example, the sequence {20, 30, 40, 50} is arithmetic because the difference between the terms is 10. To find the next term in an arithmetic sequence, add the common value to the previous term.