A finite or infinite sequence of terms a1, a2, a3,… with a common difference d, so that a2−a1 = d, a3−a2 = d, and so on. The first term is usually denoted by a. For example, 2, 5, 8, 11,…is the arithmetic sequence with a = 2, d = 3. In such an arithmetic sequence, the n-th term an is given by an = a + (n−1)d.