Question 89
Calculate the sum of the digits of the number
$$
9 \times 99 \times 9999 \times \cdots \times \underbrace{99 \ldots 99}_{2^{n}}
$$
where the number of nines in each factor doubles.
$$
9 \times 99 \times 9999 \times \cdots \times \underbrace{99 \ldots 99}_{2^{n}}
$$
where the number of nines in each factor doubles.