A sequence is a list of numbers in some order. It has first term, second term, third term, and so on. So we can think of a sequence as a function whose domain is the set of positive integers {1, 2, 3, 4, ..}

From the above activities you have seen different sequences, where some of the sequences were formed by adding a fixed number, some by multiplying by a fixed number, and some by other methods.

Definition
An arithmetic sequence or arithmetic progression is a sequence in which each term after the first term is obtained by adding a fixed number to the preceding term to find the next term.
• In arithmetic progression, the fixed number is called the common difference.