Answer:
 is an expression which describe the given sequence
Step-by-step explanation:
Arithmetic sequence states that a sequence where the difference between each successive pair of terms is the same.  
The general rule for the arithmetic sequence is given by;  
               ......[1]
where
 represents  the first term
d  represents the common difference
and n is the number of terms;
Given sequence: -1 , 0 , 1 , 2 , .....
This is an arithmetic sequence with common difference
Since, 
0-(-1) = 1
1-0 =1
2-1 = 1 ....
Here, 
Substitute the value of 
 , d =1 in [1] we get
 

Therefore,an expression which describe the given sequence is,  