Logarithmic integral
From specialfunctionswiki
The logarithmic integral is $$\mathrm{li}(x) = \displaystyle\int_0^x \dfrac{1}{\log(t)} \mathrm{d}t,$$ where $\log$ denotes the logarithm.
Domain coloring of $\mathrm{li}$.
Properties
Relationship between logarithmic integral and exponential integral
Prime number theorem, logarithmic integral