A real or complex, finite or infinite sequence a1, a2, a3,…with a common ratio r, so that a2/a1 = r, a3/a2 = r,…. The first term is usually denoted by a. For example, 3, 6, 12, 24, 48,…is the geometric sequence with a = 3, r = 2. In such a geometric sequence, the nth term an is given by an = arn−1.