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Gompertz constant

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

History
When Euler studied divergent infinite series, he encountered \delta via, for example, the above integral representation. Le Lionnais called \delta the Gompertz constant because of its role in survival analysis. This result was improved in 2012 by Tanguy Rivoal where he proved that at least one of them is transcendental. ==Identities involving the Gompertz constant==
Identities involving the Gompertz constant
The most frequent appearance of \delta is in the following integrals: : \delta = \int_0^\infty\ln(1+x)e^{-x}dx : \delta = \int_0^1\frac{1}{1-\ln(x)}dx which follow from the definition of by integration of parts and a variable substitution respectively. Applying the Taylor expansion of \operatorname{Ei} we have the series representation : \delta = -e\left(\gamma+\sum_{n=1}^\infty\frac{(-1)^n}{n\cdot n!}\right). Gompertz's constant is connected to the Gregory coefficients via the 2013 formula of I. Mező: : \delta = \sum_{n=0}^\infty\frac{\ln(n+1)}{n!}-\sum_{n=0}^\infty C_{n+1}\{e\cdot n!\}-\frac{1}{2}. The Gompertz constant also happens to be the regularized value of the summation of alternating factorials of all natural numbers (1 − 1 + 2 − 6 + 24 − 120 + ⋯), which is defined by Borel summation: : \delta = \sum_{k=0}^{\infty} (-1)^k k! It is also related to several polynomial continued fractions: : \frac1\delta = 2-\cfrac{1^2}{4-\cfrac{2^2}{6-\cfrac{3^2}{8-\cfrac{4^2}{\ddots \cfrac{n^2}{2(n+1)-\dots}}}}} : \frac1\delta = 1+\cfrac{1}{1+\cfrac{1}{1+\cfrac{2}{1+\cfrac{2}{1+\cfrac{3}{1+\cfrac{3}{1+\cfrac{4}{\dots}}}}}}} : \frac{1}{1-\delta} = 3-\cfrac{2}{5-\cfrac{6}{7-\cfrac{12}{9-\cfrac{20}{\ddots \cfrac{n(n+1)}{2n+3-\dots}}}}} ==Notes==
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