Li 2(1)=pi^2/6
From specialfunctionswiki
Theorem
The following formula holds: $$\mathrm{Li}_2(1) = \dfrac{\pi^2}{6},$$ where $\mathrm{Li}$ denotes the dilogarithm and $\pi$ denotes pi.
Proof
References
1981: Leonard Lewin: Polylogarithms and Associated Functions (2nd ed.) ... (previous) ... (next): $(1.9)$