English: Tetration by period. This is a fractal of tetration showing the points in the complex plane that are periodic under iteration. The red kidney shaped area has a period of one and is the area of convergence of the power tower function. The small yellow circle in the depression to the left of the red area is period two and contain zero. The large green area is period three. This fractal is similar to the Mandelbrot fractal except it is an exponential map instead of a quadratic map. The fractal was created using Fractint and shows from -4.5 to 3.5 of the real axis and from –3i to 3i on the imaginary axis.