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rewrote since being a good approximation to the prime-counting function is a property of the logarithmic integral function in general, not of the offset logarithmic integral function in particular |
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==Special values==
The function li(''x'') has a single positive zero; it occurs at ''x'' ≈ 1.45136 92348
Li(0) = li(2) ≈ 1.045163 780117 492784 844588 889194 613136 522615 578151… {{OEIS2C|A069284}}
This is <math>-(\Gamma\left(0,-\ln 2\right) + i\,\pi)</math> where <math>\Gamma\left(a,x\right)</math> is the [[incomplete gamma function]]. It must be understood as the [[Cauchy principal value]] of the function.
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