Question 86
Let $a_1, a_2, \dots, a_{21}$ be a permutation of $1, 2, \dots, 21$, satisfying
$$
|a_{20} - a_{21}| \geq |a_{19} - a_{21}| \geq |a_{18} - a_{21}| \geq \dots \geq |a_1 - a_{21}|.
$$
The number of such permutations is ________.
$$
|a_{20} - a_{21}| \geq |a_{19} - a_{21}| \geq |a_{18} - a_{21}| \geq \dots \geq |a_1 - a_{21}|.
$$
The number of such permutations is ________.