Which is a counterexample to the conjecture?
any number that is divisible by 3 is divisible by 9.
63
69
18
27

From the bottom up:

-- Is 27 a counter example ?  No.  It's divisible by 3 and also by 9 .

-- Is 18 a counter example ?  No.  It's divisible by 3 and also by 9 .

-- Is 69 a counter example ?  Yes !  It's divisible by 3, but not by 9 .

-- Is 63 a counter example ?  No.  It's divisible by 3 and also by 9 .