Escaping set

In mathematics, and particularly complex dynamics, the escaping set of an entire function ƒ consists of all points that tend to infinity under the repeated application of ƒ. That is, a complex number ${\displaystyle z_{0}\in \mathbb {C} }$ belongs to the escaping set if and only if the sequence defined by ${\displaystyle z_{n+1}:=f(z_{n})}$ converges to infinity as ${\displaystyle n}$ gets large. The escaping set of ${\displaystyle f}$ is denoted by ${\displaystyle I(f)}$.

...
Wikipedia