OFFSET
0,1
COMMENTS
Can be considered the value of the divergent series -0! - 1! - 2! - ... ; see Lagarias reference Section 2.5. - Harry Richman, Jun 14 2020.
LINKS
Jeffrey C. Lagarias, Euler's constant: Euler's work and modern developments, arXiv:1303.1856 [math.NT], 2013; Bull. Amer. Math. Soc., 50 (2013), 527-628.
Eric Weisstein's World of Mathematics, Exponential Integral
Eric Weisstein's World of Mathematics, Subfactorial
FORMULA
The real part of subfactorial(-1), that is the real part of Gamma(0,-1)/e.
EXAMPLE
0.6971748832350660687654786819195515953171754309543695173200548...
MATHEMATICA
RealDigits[ExpIntegralEi[1]/E, 10, 102][[1]]
PROG
(PARI) real(-eint1(-1)/exp(1)) \\ Michel Marcus, Jun 15 2020
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Jean-François Alcover, Mar 15 2017
STATUS
approved