Arithmetic progression

sequence of numbers with constant differences between consecutive numbers

In mathematics, an arithmetic progression, or arithmetic sequence, is a sequence with the property that the difference between the two terms which follow one another is constant. This is different from a geometric progression, where the ratio of change between two terms is constant.
If the initial term of an arithmetic progression is and the common difference of successive members is , then the -th term of the sequence () is given by:

A finite portion of an arithmetic progression is called a finite arithmetic progression and sometimes just called an arithmetic progression. The sum of a finite arithmetic progression is called an arithmetic series.