Mandelbrot “by hand” helper

Iterate zₙ₊₁ = zₙ² + c starting at z₀ = 0. Escape when |z| > 2.

Accepted formats: a+bi, a-bi, bi, a, spaces OK. Examples: 0, -0.75i, 0.3 - 0.2i, 1+i, -1.25+0i.