The GCD of given numbers is 51.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}459 =& 3\cdot3\cdot3\cdot17\\[8pt]663 =& 3\cdot13\cdot17\\[8pt]\end{aligned}$$(view steps on how to factor 459 and 663. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}459 =& \color{blue}{\boxed{3}}\cdot3\cdot3\cdot\color{red}{\boxed{17}}\\[8pt]663 =& \color{blue}{\boxed{3}}\cdot13\cdot\color{red}{\boxed{17}}\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 3\cdot17 = 51 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.