Quadratic Recurrence and the Mandelbrot Set

[Savant13]

I am currently studying the Mandelbrot set, and have a question about one of the statements on http://mathworld.wolfram.com/QuadraticMap.html" .

It says the recurrence for the Mandelbrot set "is not in general solvable in closed form." What does this mean?

 

[Hootenanny]

From the same website: http://mathworld.wolfram.com/Closed-FormSolution.html