OFFSET
0,1
FORMULA
Equals (6 e^(1/4) - 5 Sqrt(Pi) erfi(1/2))/(8 e^(1/4)).
Equals 1F1(2;1/2;-1/4). - R. J. Mathar, Aug 27 2024
EXAMPLE
0.219454520622472130082447059387913036129463153300...
MATHEMATICA
s = Sum[(-1)^k (k + 1)!/(2 k)!, {k, 0, Infinity}]
d = N[s, 100]
First[RealDigits[d]]
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Clark Kimberling, Apr 27 2024
STATUS
approved