Gompertz constant

In mathematics, the Gompertz constant or Euler–Gompertz constant, denoted by ${\displaystyle \delta }$, appears in integral evaluations and as a value of special functions. It is named after Benjamin Gompertz.

It can be defined via the exponential integral as:

${\displaystyle \delta =-e\operatorname {Ei} (-1)=\int _{0}^{\infty }{\frac {e^{-x}}{1+x}}dx.}$

The numerical value of ${\displaystyle \delta }$ is about

δ = 0.596347362323194074341078499369...   (sequence A073003 in the OEIS).