A group of numbers connected by a definite law is known as sequence.

Arithmetic Progression

A Sequence in which each term is obtained from the preceeding term by adding a constant quantity to it.

A sequence is called a series if its terms are connected by the sign of addition or subtraction.

nth term of an Arithmetic Progression

an = a + (n - 1) d = l

where a is first term and d is common difference l is last term.