The original Skewes number was merely an upper bound before which the condition Li(x)<pi(x) must occur at least once; this number (Sk_{1}) was e^{(e^(e^79))}, or roughly 10^{(10^(10^34))}, in 1912. By 1987, this number was reduced to approximately 8.185*10^{370}. Both of these numbers depend on the Riemann hypothesis being true. Sk_{2} is the upper bound if the Riemann hypothesis is false; it is estimated to be 10^{(10^(10^(10^3)))}.

*Source: http://mathworld.wolfram.com/SkewesNumber.html*