Studying  about  number  sequences  is  helpful  to  make  predictions  in  the  patterns  of natural events.

An ordered set of numbers such as  is called a sequence and usually designated briefly by  

Each number  is a term of the sequence.

In particular the nth term of a sequence is denoted by   

Definition: A sequence is a function whose domain is the collection of all integers greater than by or equal to a given integer m(usually 0 or 1).

Observe if we define a function by