The GCD of given numbers is 53.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}106 =& 2\cdot53\\[8pt]159 =& 3\cdot53\\[8pt]265 =& 5\cdot53\\[8pt]\end{aligned}$$(view steps on how to factor 106, 159 and 265. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}106 =& 2\cdot\color{blue}{\boxed{53}}\\[8pt]159 =& 3\cdot\color{blue}{\boxed{53}}\\[8pt]265 =& 5\cdot\color{blue}{\boxed{53}}\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 53 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.