Is G isomorphic to $\mathbb{Z} \oplus \mathbb{Z}$? If $ G=\{3^{m}6^{n}|m,n \in \mathbb{Z}\}$ under multiplication then i want prove that this G 
is isomorphic to $\mathbb{Z} \oplus \mathbb{Z}$.Can any one help me to solve this example?
please help me. thanks in advance. 
Can i define $\phi:\mathbb{Z} \oplus \mathbb{Z} to G$ 
as $\phi\big((m,n)\big)=3^m 6^n$

Hint: $2^k=3^{-k}6^k$.${}{}{}{}{}{}{}{}$
