>53

Li_k(z) ≡ Σ[n=1,∞) (z^n)/(n^k),

Li_2(1/2) = (1/12)π^2 - (1/2){ln(2)}^2
　　　　　= 0.582240526465012505902656320159680108755…

Li_3(1/2) = (7/8)ζ(3) - (1/12)(π^2)ln(2) + (1/6){ln(2)}^3
　　　　　= 0.537213193608040200940623225594965826675…

http://functions.wolfram.com/ZetaFunctionsandPolylogarithms/PolyLog/03/02/02/