A019875 Decimal expansion of sine of 66 degrees.

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

Offset

0,1

Comments

A quartic number with denominator 2. - Charles R Greathouse IV, Aug 27 2017

Links

Ivan Panchenko, Table of n, a(n) for n = 0..1000

Wikipedia, Exact trigonometric constants

Index entries for algebraic numbers, degree 4

Formula

Equals cos(2*Pi/15) = 2*A019887^2 - 1 = 1 - 2*A019821^2. - R. J. Mathar, Jun 18 2006

Equals 2*A019842*A019866. - R. J. Mathar, Jan 17 2021

Largest of the 4 real-valued roots of 16*x^4-8*x^3-16*x^2+8*x+1=0. (Other A019851, -A019815, -A019887). - R. J. Mathar, Sep 04 2025

Example

0.913545457...

Mathematica

RealDigits[N[Cos[2*Pi/15], 110]][[1]] (* Wesley Ivan Hurt, Dec 27 2021 *)
RealDigits[Sin[66 Degree], 10, 120][[1]] (* Harvey P. Dale, Nov 25 2025 *)

Prog

(PARI) cos(2*Pi/15) \\ Charles R Greathouse IV, Aug 27 2017

Crossrefs

Cf. A019821, A019842, A019866, A019887.

Sequence in context: A154181 A334479 A239121 * A388836 A381695 A388674

Adjacent sequences: A019872 A019873 A019874 * A019876 A019877 A019878

Keyword

nonn,cons

Author

N. J. A. Sloane

Status

approved