A negated right arrow symbol indicating non-implication or the absence of a mapping between mathematical objects.
Examples
Showing a function is not a mapping between sets
f: A \nrightarrow B \text{ indicates f is not a function from A to B}
Logical statement showing non-implication
P \nrightarrow Q \text{ means P does not imply Q}
Example in number theory
n > 2 \nrightarrow n \text{ is prime}