The GCD of given numbers is 33.
Step 1 : Find prime factorization of each number.
$$\begin{aligned}753951 =& 3\cdot11\cdot11\cdot31\cdot67\\[8pt]159753 =& 3\cdot11\cdot47\cdot103\\[8pt]\end{aligned}$$(view steps on how to factor 753951 and 159753. )
Step 2 : Put a box around factors that are common for all numbers:
$$\begin{aligned}753951 =& \color{blue}{\boxed{3}}\cdot\color{red}{\boxed{11}}\cdot11\cdot31\cdot67\\[8pt]159753 =& \color{blue}{\boxed{3}}\cdot\color{red}{\boxed{11}}\cdot47\cdot103\\[8pt]\end{aligned}$$Step 3 : Multiply the boxed numbers together:
$$ GCD = 3\cdot11 = 33 $$This solution can be visualized using a Venn diagram.
The GCD equals the product of the numbers at the intersection.