An integer sequence may be specified *explicitly* by giving a formula for its *n*-th term, or *implicitly* by giving a relationship between its terms. For example, the sequence 1, 1, 2, 3, 5, 8, 13, ... (the Fibonacci sequence) is formed by starting with two ones and then adding any two consecutive terms to obtain the next one: an implicit description. The sequence 0, 3, 8, 15, ... is formed according to the formula *n*^{2} - 1 for the *n*-th term: an explicit definition.