Up and down in odd numbers

Question

What is up and down in odd numbers but can only be 4 digits?

Answer 1

Okay, the question is a bit unclear but here is a plausible solution:

We were given 1, 3, 5, 7, and 9 to form a 4-digit number by going only up or down the number line.

One way to form that would be:

1. 1 3 5 7
2. 3 5 7 9
3. 9 7 5 3
4. 7 5 3 1

In each 4-digit number generated, each digit is reduced by 2 to get the next digit. Hopefully, that explains the question.