That will be a very big data.
if a variable has length 3=3*8 bytes=24 bytes which I think is the minimum length on PC or unix.
4**20*(4*24)=105,553,116,266,496 bytes

没考虑周到，修改过了，顺便问一句，为啥是（4*24）？

one variable needs 3*8=24 bytes. four variables need 4*24

怎么写程序，能否指导下，谢谢？

The question is too general and too big.

For your particular question, I think the fastest way is,


data need;
  do var1=0,1,3,7;
     do var2=0,1,3,7;
            do var3=0,1,3,7;
                  do var4=0,1,3,7;
                     do var5=0,1,3,7;
                            output;
                         end;
                  end;
                end;
         end;
        end;
run;

I only do five variables, same logic will do more variables. Since it is a Cartesian product, the needed space grows up quickly.