I am trying to find the smallest subring of rationals containing $p/q$, where p,q are relatively prime. I am constructing the subring from $p/q $ and I think rationals of form $pZ/q^k$ where k is whole number is the answer. Am I wrong? Is there any general solution for $p/q$?
Edit: I am looking for a general solution for any $p/q$. There is no constraint that 1 should be in the subring.