Skip over navigation  Sequences and Series  General Sequences
and Series  Terms and Formulae   A sequence is a function whose
domain is the positive integers. The value of the function at a
given integer is a term of the sequence. The range of a sequence
is the set of its terms. Sequences are not typically written as
ordered pairs, or drawn as graphs; a sequence is most often
represented by a list of its terms starting with the first term,
followed by the second, and so on. A general sequence looks
something like this: a 1, a 2, a 3,…, a n , where n is an
integer, and a n is the n th term of the sequence. A sequence
can also be written as a formula for which any integer can be
the input, and the corresponding term is the output.  Here is an
example sequence: a n = 2n = 2, 4, 6, 8, 10,… , where n is an
integer. The formula a n = 2n is called an explicit formula for
the sequence. By plugging any integer n into the explicit
formula for the sequence, the n th term can be found.   When a
sequence is given by an ex