From the coordinates, we can name out the following terms
a2 = 1
a3 = 3
a4 = 9
The terms belong to a geometric progression with a common ratio of 3.
Solving for the first term or a1
a2 = a1 r^(n-1)
1 = a1 (3)^!
a1 = 1/3
So, the sequence has the equation
an = (1/3) (3)^(n-1)
The answer is the THIRD OPTION.