A371935 -id:A371935 - cp's OEIS frontend

A371936 Decimal expansion of Sum_{k>=0} (-1)^k / (2(k+1)(2*k+1)!).

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

Offset: 0

Clark Kimberling, Apr 24 2024

			0.459697694131860282599063392557023396267689579382077772...

Cf. A049470, A206533, A371935.

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

1 - cos(1) \\ Stefano Spezia, Apr 21 2025

Equals 1 - cos(1) = A371935/2 = 1 - A049470.

Equals 1/A206533. - Hugo Pfoertner, Apr 26 2024

A272795 Decimal expansion of 2*sin(1/2).

Original entry on oeis.org

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

Offset: 0

Peter M. Chema, May 22 2016

The length of the line underlying an arc of one radian with radius 1 (i.e., the linear distance for ends of an arc length 1 having same length as radius).

			0.958851077208406000546575870431142776163606735881201350377...

Cf. A201504, A371935.

RealDigits[2 Sin[1/2], 10, 100][[1]] (* Ilya Gutkovskiy, May 22 2016 *)

2*sin(1/2) \\ Stefano Spezia, Apr 21 2025

Equals i*e^(-i/2) - i*e^(i/2).
Equals 2*A201504.
Equals Sum_{k>=0} 2*(-1)^k*(1/2 - Pi/2)^(2*k)/(2*k)!. - Ilya Gutkovskiy, May 22 2016
Equals sqrt(A371935). - Hugo Pfoertner, Apr 21 2025

More digits from Jon E. Schoenfield, Mar 15 2018

cp's OEIS Frontend

A371936 Decimal expansion of Sum_{k>=0} (-1)^k / (2(k+1)(2*k+1)!).

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A272795 Decimal expansion of 2*sin(1/2).

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PARI

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Extensions

cp's OEIS Frontend

A371936 Decimal expansion of Sum_{k>=0} (-1)^k / (2*(k+1)*(2*k+1)!).

Views

Author

Keywords

Examples

Crossrefs

Programs

Mathematica

PARI

Formula

A272795 Decimal expansion of 2*sin(1/2).

Views

Author

Keywords

Comments

Examples

Crossrefs

Programs

Mathematica

PARI

Formula

Extensions

A371936 Decimal expansion of Sum_{k>=0} (-1)^k / (2(k+1)(2*k+1)!).