A019688 -id:A019688 - cp's OEIS frontend

A019702 Decimal expansion of 2*Pi/21.

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

Offset: 0

N. J. A. Sloane

Pi/105 = 0.1 * 2*Pi/21 is the mean area of the triangles that can be formed by breaking a unit-length stick in 3 parts, by uniformly and independently choosing 2 points on it (taking only those cases in which the 3 parts can form a triangle) (Mathai, 1999). - Amiram Eldar, Jul 28 2020

			0.299199300341885070329775560312333608018778038035724...

A. M. Mathai, An Introduction to Geometrical Probability: Distributional Aspects with Applications, CRC Press, 1999. See example 2.5.3, pp. 269-270.

Ivan Panchenko, Table of n, a(n) for n = 0..1000
Index entries for transcendental numbers

Equals twice A019688.

Cf. A000796.

RealDigits[2*Pi/21, 10, 100][[1]] (* Amiram Eldar, Jul 28 2020 *)

2*Pi/21 \\ Charles R Greathouse IV, Oct 01 2022

A387454 Decimal expansion of cos(Pi/21).

Original entry on oeis.org

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

Offset: 0

R. J. Mathar, Aug 29 2025

			0.98883082622512854507...

R. J. Mathar, Reduction formulas of the cosine of integer fractions of pi, (2008) vixra:2210.0026
Index entries for algebraic numbers, degree 6

Cf. A019688.

Equals sin(19/42*Pi).
Largest of the 6 real-valued roots of 64*x^6+32*x^5-96*x^4-48*x^3+32*x^2+16*x+1=0.
4*this^3 -3*this = A073052.
Equals 2F1(-1/14,1/14;1/2;3/4). - R. J. Mathar, Aug 31 2025

cp's OEIS Frontend

A019702 Decimal expansion of 2*Pi/21.

Views

Author

Keywords

Comments

Examples

References

Links

Crossrefs

Programs

Mathematica

PARI