Javascript Function using RegEx Regular Expression

I need to check client side if a DropDownList.SelectedItem.Value is any of the following: 1,3,9,17,or 15.


Rather than use a clumsy if statement, I do this by seeing if the value will match a Regular Expression:

      function taskChange() {
      var task = $get("ddlTest");
      var RegExp = "(^1$^3$^9$^17$^15$)" ;
      if (RegExp.match(task.value))
           { 
               // A value of 1,3,9,17,or 15 was selected

               // do whatever 

           }
           else
           {
                //Some other value was selected 

                // do whatever
           }
       }