There's a q Mandelbrot here:

https://github.com/indiscible/qmandel

And Arthur's version in k (also below):

http://www.kparc.com/z/comp.k

I should convert it to k9 (Shakti)...

    +/~^+/b*b:49{c+(-/x*x;2**/x)}/c:-1.5 -1+(2*!2#w)%w:10