An arithmetic sequence is a sequence that adds a constant from one term to the next. The common value added or subtracted between two successive terms of an arithmetic sequence is called the common difference, d.

An example of an arithmetic sequence is 4, 7, 10, 13, 16 … and the common difference of this sequence is 3. To change one term to the next in the sequence, add three.

In general, the terms of a sequence are written as: a1, a2, a3, a4 ...anwhere a1 is the first term in the sequence, a2is the second term in the sequence, a3 is the third term in the sequence, and an is the nth term in the sequence. It is called the nth term because sequences will have a varying number of terms.