Step 1 :
Divide $ 3921 $ by $ 23 $ and get the remainder

$$ 3921 : 23 = 170 \text{ ( remainder is } \color{blue}{ 11 } \text{ ) } $$

The remainder is positive ($ 11 > 0 $), so we will continue with division.

Step 2 :
Divide $ 23 $ by $ \color{blue}{ 11 } $ and get the remainder

$$ 23 : 11 = 2 \text{ ( remainder is } \color{blue}{ 1 } \text{ ) } $$

The remainder is still positive ($ 1 > 0 $), so we will continue with division.

Step 3 :
Divide $ 11 $ by $ \color{blue}{ 1 } $ and get the remainder

$$ 11 : \color{blue}{ \boxed { 1 }} = 11 \text{ ( remainder is } \color{blue}{ 0 } \text{ ) } $$

The remainder is zero => GCD is the last divisor $ \color{blue}{ \boxed { 1 }} $.

This solution can be visualized using a Venn diagram.

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

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