Answer:
5, 9, 15,....is not an arithmetic sequence.
Step-by-step explanation:
Arithmetic sequence is a sequence in which difference between the consecutive terms is constant.
Example: 0 , 5, 10, 15, 20 is an arithmetic sequence with common difference of 5 between the terms.
Consider the given sequence,
5, 9, 15,....
Here, 
We first find the difference between the terms,


Since the difference is not constant .
So,it is not an arithmetic sequence.