$$
\underbrace{2 \times 2 \times \ldots \times 2}_{20 \uparrow 2}-1
$$

The result's units digit is $\qquad$
【Answer】 5
Analysis: $2 \div 10$ remainder is $2,(2 \times 2) \div 10$ remainder is $4,(2 \times 2 \times 2) \div 10$ remainder is $8,(2 \times 2 \times 2 \times 2) \div 10$ remainder is 6, that is, 4 twos multiplied together form one cycle, $20 \div 4=5$, so $\underbrace{2 \times 2 \times \ldots \times 2}_{20 \text { twos }}$ remainder is 6,
$$
\underbrace{2 \times 2 \times \ldots \times 2}_{20 \uparrow 2}-1
$$
$\div 10$ remainder is 5