Skewes' number

Etymology
Named after South African mathematician.

Noun

 * 1)  Any of several extremely large numbers used as upper bounds for the smallest natural number $$x$$ for which $$\pi(x) > \operatorname{li}(x)$$, where $$\pi$$ is the  and $$li$$ is the logarithmic integral function. These bounds have since been improved by others.