Conditional Cell protection
 

I would like to blank and protect certain cells depending on a value in one
cell (A1).

If, e.g. the value in cell A1 is 6, then the users are only allowed to enter
values in the first 6 weeks for that year (=first 6 columns in the table). In
order to avoid problems I would like to erase all existing data in columns
7-- and then lock these cells. Any ideas how to do this?