Using the Ratio Test gives the convergence of the series if
`lim(n->oo) |a_(n+1)/a_n| < 1`
= `lim(n->oo) a^(n+1 - n)/2^(n+1 - n)`
= `lim(n->oo) a/2`
`a/2` is less than, equal to or greater than 1 depending on what the value of a is. Here, the value of a is not given.
It is not possible to determine if the given series is convergent using the Ratio Test.