A2:4，

A3: 16/3

A4:64/9

The side length of each division is 1/3, and the number of sides is four times that of the last one.

(Divide each side of A 1 into three equal parts, make an equilateral triangle outward on the middle line segment, and record the figure obtained after removing the middle line segment as A2;

The above contents show that each side becomes four sides, and the side length is the original 1/3, that is, A2 has 12 sides, each side is 1/3, and the circumference of A2 is 12*( 1/3)=4.