Arithmetic progression

In mathematics, an arithmetic progression, or arithmetic sequence, is a sequence. The difference between each two terms which follow one another is always the same. 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 ${\displaystyle a_{1}}$ and the common difference is ${\displaystyle d}$, then the ${\displaystyle n}$-th term of the sequence (${\displaystyle a_{n}}$) is given by:

${\displaystyle a_{n}=a_{1}+(n-1)d}$

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.