https://en.wikipedia.org/wiki/Mandelbrot_set
https://csl.name/mandelbrot/

The Mandelbrot set is the set of complex numbers {\displaystyle c} c for which the function {\displaystyle f_{c}(z)=z^{2}+c} {\displaystyle f_{c}(z)=z^{2}+c} does not diverge when iterated from {\displaystyle z=0} z=0, i.e., for which the sequence {\displaystyle f_{c}(0)} {\displaystyle f_{c}(0)}, {\displaystyle f_{c}(f_{c}(0))} {\displaystyle f_{c}(f_{c}(0))}, etc., remains bounded in absolute value.