What is the explicit rule for this geometric sequence?29,23,2,6,...an=29⋅3nan=3(29)n−1an=3(29)nan=29⋅3n−1

What is the explicit rule for this geometric sequence?

29,23,2,6,...

For n=0 we have 
an=29⋅3n=0≠29
an=3(29)n−1= -1≠29
an=3(29)n=0≠29
an=29⋅3n−1=-1≠29

And 
For n=1 we have 
an=29⋅3n=78≠29
an=3(29)n−1=77≠29
an=3(29)n=78≠29
an=29⋅3n−1=-77≠29

All four formulas are non-correct