Writing a value in a specific cell (number=line)

Ok. So here's the deal. All i want to do is when i write a number, "7" for example in cell B2 then automatically the value 2 is written in cell B7. If i write "14" then the value 2 is written in cell B14 etc.

So the number that i am writing is actually the number of the line that i need to write a value too.

If also you can make it work backwards it would be really nice.

Thank you for your time.