Definition:Arithmetic Sequence

Definition
An arithmetic progression is a sequence $\left \langle{a_n}\right \rangle$ in $\R$ defined as:
 * $a_n = a_0 + n d$ for $n = 0, 1, 2, \ldots$

Thus its general form is:
 * $a_0, a_0 + d, a_0 + 2 d, a_0 + 3 d, \ldots$

Also known as
The term arithmetical progression is sometimes seen.

Linguistic Note
In this context, the word arithmetic is pronounced with the stress on the first and third syllables: a-rith-me-tic, rather than on the second syllable: a-rith-me-tic.

This is because the word is being used in its adjectival form.