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%I #13 Aug 02 2024 12:26:23
%S 7,1,2,2,1,8,1,9,1,7,5,1,0,1,1,1,4,7,9,6,7,0,2,1,1,7,6,2,4,4,8,3,4,7,
%T 8,5,5,4,8,2,1,4,7,3,8,6,7,9,8,4,6,0,1,9,0,7,5,6,6,9,8,4,8,3,1,6,6,2,
%U 2,5,7,7,3,7,9,7,9,5,9,7,3,8,0,8,3,8
%N Decimal expansion of Sum_{k>=0} (-1)^k * (k+1)! / (2k+1)!.
%F Equals (2*e^(1/4) + sqrt(Pi)*erfi(1/2))/(4*e^(1/4)).
%F Equals 1F1(2;3/2;-1/4) . - _R. J. Mathar_, Aug 02 2024
%e 0.712218191751011147967021176244834785548214...
%t s = Sum[(-1)^k (k + 1)!/(2 k+1)!, {k, 0, Infinity}]
%t d = N[s, 100]
%t First[RealDigits[d]]
%Y Cf. A371941.
%K nonn,cons
%O 0,1
%A _Clark Kimberling_, Apr 28 2024