Task
Produce an ASCII representation of a Sierpinski triangle of order   N.



Example
The Sierpinski triangle of order   4   should look like this:

                       *
                      * *
                     *   *
                    * * * *
                   *       *
                  * *     * *
                 *   *   *   *
                * * * * * * * *
               *               *
              * *             * *
             *   *           *   *
            * * * *         * * * *
           *       *       *       *
          * *     * *     * *     * *
         *   *   *   *   *   *   *   *
        * * * * * * * * * * * * * * * *



Related tasks
 Sierpinski triangle/Graphical for graphics images of this pattern. 
 Sierpinski carpet


|=  n=@ud
=+  m=0
=+  o=(reap 1 '*')
|^  ?:  =(m n)  o
    $(m +(m), o (weld top bot))
++  gap  (fil 3 (pow 2 m) ' ')
++  top  (turn o |=(l=@t (rap 3 gap l gap ~)))
++  bot  (turn o |=(l=@t (rap 3 l ' ' l ~)))
--