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

%I #15 Apr 27 2024 08:38:47

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

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

%U 9,2,1,0,4,5,1,0,5,6,4,7,0,9,6,4,0,9

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

%F Equals 2*(1 - cos(1)) = 2 * A371936.

%F From _Hugo Pfoertner_, Apr 26 2024: (Start)

%F Equals A243596/Pi.

%F Equals A272795^2. (End)

%e 0.91939538826372056519812678511404679253...

%t s = N[Sum[(-1)^k/((k + 1) (2 k + 1)!), {k, 0, Infinity}], 120]

%t First[RealDigits[s]]

%Y Cf. A049470, A243596, A272795, A371936.

%K nonn,cons

%O 0,1

%A _Clark Kimberling_, Apr 24 2024