https://functions.wolfram.com/GammaBetaErf/ExpIntegralEi/13/01/
Exponential integral Ei: Differential equations (subsection 13/01)
Ordinary linear differential equations and wronskians (14 formulas)
exponential integraldifferential equationssubsection
https://www.boost.org/doc/libs/latest/libs/math/doc/html/math_toolkit/expint/expint_n.html
Exponential Integral En
exponential integral