In the number sequence 8 4 1 5 6 3 2 7 9 4 5 2, if all the odd numbers are decreased by one and all the even numbers are increased by one, and then the newly formed sequence is arranged in descending order, which digit will be ninth from the left?

How many pairs of digits are there in the number '58391746', such that the number of digits between them is the same as the number of digits between them in the natural number series (in both forward and backward directions)?

In the following series, counted from left to right: 2 5 3 1 1 8 1 7 9 9 4 8 2 7 5 0 5 7 5 3 7 0 5 8 3 4 2 4 8 1 How many odd numbers are there, each of which is immediately preceded by an odd number and immediately followed by an even number?