20. There is a sequence of numbers, the first number is 1, the second number is 3, starting from the third number, each number is exactly twice the sum of the previous two numbers:
$$
1,3,8,22,60,164,448,
$$
$\qquad$
In this sequence, the remainder when the 2000th number is divided by 9 is $\qquad$ .
Answer: 3