Question 21
A list of $8$ numbers is formed by beginning with two given numbers. Each new number in the list is the product of the two previous numbers. Find the first number if the last three are $16,$ $64,$ $1024$:
$$
?, \underline{\phantom{x}}, \underline{\phantom{x}}, \underline{\phantom{x}}, \underline{\phantom{x}}, 16, 64, 1024
$$
$$
?, \underline{\phantom{x}}, \underline{\phantom{x}}, \underline{\phantom{x}}, \underline{\phantom{x}}, 16, 64, 1024
$$