Answer:
Option 3 is correct that is all integers where n ≥ 1
Step-by-step explanation:
We have been given the arithmetic sequence 
Here, domain are the values that n can take
Therefore, option 3 is correct.
Option 1 is incorrect because arithmetic series will start from 1
Option 2 is incorrect because it is not considering the positive values except 1
Option 4 is incorrect because if it will be real number range may be a fraction which should not be in an arithmetic sequence.