What does the variable n usually represent in mathematics?

What does the variable n in mathematics usually mean?

The variable can mean many things.  

1)  Maybe the variable is used in an equation only to represent an unknown, such as:  `10 = 6n+4`

2)  The variable "n" can often be used to represent a number, or element in a sequence.  Often written as 

`a(n) = 4n+5 `

represents an arithmetic sequence of values where n represents the number of the element.

3) It is also used to represent integer elements of a set. So the set of even numbers has elements n= 2, n= 4, n=6, etc.