Step 1 :
Divide $ 5397 $ by $ 133 $ and get the remainder

$$ 5397 : 133 = 40 \text{ ( remainder is } \color{blue}{ 77 } \text{ ) } $$

The remainder is positive ($ 77 > 0 $), so we will continue with division.

Step 2 :
Divide $ 133 $ by $ \color{blue}{ 77 } $ and get the remainder

$$ 133 : 77 = 1 \text{ ( remainder is } \color{blue}{ 56 } \text{ ) } $$

The remainder is still positive ($ 56 > 0 $), so we will continue with division.

Step 3 :
Divide $ 77 $ by $ \color{blue}{ 56 } $ and get the remainder

$$ 77 : 56 = 1 \text{ ( remainder is } \color{blue}{ 21 } \text{ ) } $$

The remainder is still positive ($ 21 > 0 $), so we will continue with division.

Step 4 :
Divide $ 56 $ by $ \color{blue}{ 21 } $ and get the remainder

$$ 56 : 21 = 2 \text{ ( remainder is } \color{blue}{ 14 } \text{ ) } $$

The remainder is still positive ($ 14 > 0 $), so we will continue with division.

Step 5 :
Divide $ 21 $ by $ \color{blue}{ 14 } $ and get the remainder

$$ 21 : 14 = 1 \text{ ( remainder is } \color{blue}{ 7 } \text{ ) } $$

The remainder is still positive ($ 7 > 0 $), so we will continue with division.

Step 6 :
Divide $ 14 $ by $ \color{blue}{ 7 } $ and get the remainder

$$ 14 : \color{blue}{ \boxed { 7 }} = 2 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 7 }} $.

This solution can be visualized using a Venn diagram.

The GCD equals the product of the numbers at the intersection.

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