The Mandelbulb is a 3-dimensional fractal: since a canonical 3-dimensional Mandelbrot set does not exist, it is possible to construct Mandelbrot sets in 4 dimensions using quaternions & bicomplex numbers https://buff.ly/2KyGDuj | https://buff.ly/2FDjR0J | https://buff.ly/2KyUp0a pic.twitter.com/MdRtLHkGEN
It means: when you take pairs of numbers that describe 2D coordinates, you can make a simple function that produces the 2D Mandelbrot fractal. No such function exists for 3D coordinates. But for 4D coordinates it works again (the animation is 3D, with the 4th dimension as time).