SQL & PL/SQL

Hello Everybody
I was trying to create a procedure for the calculation of factorail of a number
but something is not going right
I hope you guys can lead to the correct path
here is my code

create or replace procedure factorial(n in number)
is 
           v number;
begin

       for i in reverse n..1
 loop
              v :=v*i;
end loop;
dbms_output.put_line(v);
end;