how to fill in cell a1 with a number and have b1 automatically fill with different number

I don't know if you can help me or not, but thought I would give it a try! I do a lot of work in excel and can maneuver the program pretty well. What I can't figure out is HOW to do one thing...

Don't know how to visually show u what I am trying to do is but when I fill in cell A1 with 1 AND I would like for B1 to automatically fill in with the number 7. I'd like to have it done for numbers 1-6 and column b to automatically fill in with numbers from 7-1.. but I can't figure out if or how I can do that without having to do the placings in column A and going back to fill in points in column B.


If you can provide me with the direction on how to create this, I would really really appreciate it! Thanks in advance for all responses!

Amy