A019890 Decimal expansion of sine of 81 degrees.

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

Offset

0,1

Comments

Also the real part of i^(1/10). - Stanislav Sykora, Apr 25 2012

Equals sin(9*Pi/20). - Wesley Ivan Hurt, Sep 01 2014

An algebraic number of degree 8 and denominator 2. - Charles R Greathouse IV, Aug 27 2017

Links

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

Wikipedia, Trigonometric constants expressed in real radicals

Index entries for algebraic numbers, degree 8

Formula

Equals cos(Pi/20) = sqrt((1+A019881)/2) = sqrt(1-A019818^2) = sqrt(5-sqrt(5))*(sqrt(5)+sqrt(5+2*sqrt(5)))/(4*sqrt(5)). - R. J. Mathar, Jun 18 2006

Equals A019863 * A019872 + A019836 * A019845 = A019887 * A019896 + A019812 * A019821. - R. J. Mathar, Jan 27 2021

Root of 256*x^8 -512*x^6 +304*x^4 -48*x^2+1=0. - R. J. Mathar, Aug 29 2025

Equals 2F1(-1/10,1/10;1/2;1/2). - R. J. Mathar, Aug 31 2025

Example

0.98768834059513772619004024769343726075840686158988043492390480163...

Maple

Digits:=100: evalf(sin(9*Pi/20)); # Wesley Ivan Hurt, Sep 01 2014

Mathematica

RealDigits[Sin[81 Degree], 10, 120][[1]] (* Harvey P. Dale, Aug 11 2012 *)

Prog

(PARI) sin(9*Pi/20) \\ Charles R Greathouse IV, Aug 27 2017

Crossrefs

Sequence in context: A390629 A363249 A107927 * A066666 A369763 A347201

Adjacent sequences: A019887 A019888 A019889 * A019891 A019892 A019893

Keyword

nonn,cons

Author

N. J. A. Sloane

Status

approved