<image>The following mathematical problem needs to be translated to English, retaining the  placeholder. Here is the translated result:

Figure (1) is a black equilateral triangle. By sequentially connecting the midpoints of its three sides, we obtain the second figure as shown in Figure (2) (its middle is a white equilateral triangle). Repeat the above method for each black equilateral triangle in Figure (2) to get the third figure as shown in Figure (3). Continue this process, and in the sixth obtained figure, the number of white equilateral triangles is ___.
