Any number that is divisible by 3 is also divisible by 6.
find a counterexample to show that the conjecture is false.
21
18
24
12

21/3=7
but
21/6=3.5

21/3 = 7        21/6 = 3.5
18/3 = 6        18/6 = 3
24/3 = 8        24/6 = 4
12/3 = 4        12/6 = 2

Each can be divided to obtain an integer, except:

21/6 = 3.5

So, while 21 can be divided by 3, it cannot be divided by 6 (for an integer anyway)