A371940 - OEIS

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A371940

Decimal expansion of Sum_{k>=0} (-1)^k (k+2)! / (2k)!.

1, 5, 0, 1, 1, 8, 2, 3, 2, 7, 2, 3, 9, 3, 2, 1, 3, 3, 3, 3, 0, 9, 8, 3, 5, 2, 8, 2, 5, 4, 7, 7, 8, 2, 7, 5, 9, 3, 4, 6, 0, 0, 5, 3, 5, 7, 3, 4, 2, 1, 0, 8, 4, 7, 7, 6, 2, 8, 0, 7, 9, 7, 2, 6, 2, 2, 6, 9, 0, 7, 0, 9, 0, 7, 1, 4, 5, 4, 3, 6, 5, 7, 6, 7, 9, 7

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OFFSET

0,2

LINKS

Table of n, a(n) for n=0..85.

FORMULA

Equals (30 e^(1/4) - 41 sqrt(Pi) erfi(1/21))/(32 e^(1/4)).

Equals 2* 1F1(3;1/2;-1/4). - R. J. Mathar, Aug 02 2024

EXAMPLE

-0.1501182327239321333309835282547782759346005...

MATHEMATICA

s = Sum[(-1)^k (k + 2)!/(2 k)!, {k, 0, Infinity}]