Skewes number

The Skewes Number, written $$Sk_1$$, is the largest number where $$\pi(n) < li(n)$$ is true, assuming the solution to the Riemann hypothesis is true. Here, $$\pi(n)$$ is the prime counting function and $$li(n)$$ is the logarithmic integral.

The original upper bound for the number was $$e^{e^{e^{79}}} \approx 10^{10^{10^{34}}}$$, in the vicinity of the googolduplex.