Question

For the series n=13 to infinity (3^n/(2n)!) use the ratio test to Find the ratio of successive terms. Write your answer as a fully simplified fraction for n >= 13

So, (3^(n+13))/(2(n+13))!) * (2n)!/3^n

Gives me 3^13/(2(n+13))

Why is this wrong? Detailed explanation preferred.