A019889 Decimal expansion of sine of 80 degrees = cos(Pi/18).

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

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• cons
• changed

Examples

			0.9848077530122080593667430245895230136706432517198424187900...
		

Links

• Ivan Panchenko, Table of n, a(n) for n = 0..1000
• Index entries for algebraic numbers, degree 6

Crossrefs

Cf. A019849, A019859.

Programs

Maple

Digits:=100: evalf(sin(4*Pi/9)); # Wesley Ivan Hurt, Sep 01 2014

Mathematica

RealDigits[ Cos[Pi/18], 10, 111] (* Robert G. Wilson v *)
RealDigits[Sin[80 Degree],10,120][[1]] (* Harvey P. Dale, Apr 16 2022 *)

PARI

real(I^(1/9)) \\ Michel Marcus, Nov 29 2013

Formula

Equals 2F1(7/12,5/12;1/2;3/4) / 2. - R. J. Mathar, Oct 27 2008

Also the real part of I^(1/9). - Stanislav Sykora, Nov 29 2013

Equals sin(4*Pi/9). - Wesley Ivan Hurt, Sep 01 2014

Equals 2*A019849*A019859. - R. J. Mathar, Jan 17 2021

Largest positive root of 64*x^6 - 96*x^4 + 36*x^2 - 3. - Artur Jasinski, May 09 2025

Other roots are +- A019849 and +- A019829. - R. J. Mathar, Aug 29 2025

4*this^3 -3*this = A010527. - R. J. Mathar, Aug 29 2025

Equals 2F1(-1/12,1/12; 1/2 ; 3/4). - R. J. Mathar, Aug 31 2025