

A019827


Decimal expansion of sin(Pi/10) (angle of 18 degrees).


16



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

0,1


COMMENTS

Decimal expansion of cos(2*Pi/2) (angle of 72 degrees).
Also the imaginary part of i^(1/5).  Stanislav Sykora, Apr 25 2012
One of the two roots of 4x^2 + 2x  1 (the other is the sine of 54 degrees times 1).  Alonso del Arte, Apr 25 2015
This is the height h of the isosceles triangle in a regular pentagon inscribed in a unit circle, formed by a diagonal as base and two adjacent radii. h = cos(2*Pi/5) = sin(Pi/10).  Wolfdieter Lang, Jan 08 2018


LINKS

Zak Seidov, Table of n, a(n) for n = 0..999
Wikipedia, Exact trigonometric constants


FORMULA

Equals (sqrt(5)  1)/4 = (phi  1)/2 = 1/(2*phi), with phi from A001622.
Equals 1/(1 + sqrt(5)).  Omar E. Pol, Nov 15 2007


EXAMPLE

0.3090169943749474241022934171828190588601545899028814310677243113526306...


MATHEMATICA

RealDigits[Sin[18 Degree], 10, 108][[1]] (* Alonso del Arte, Apr 20 2015 *)


PROG

(PARI) sin(Pi/10) \\ Charles R Greathouse IV, Feb 03 2015
(PARI) polrootsreal(4*x^2 + 2*x  1)[2] \\ Charles R Greathouse IV, Feb 03 2015


CROSSREFS

Cf. A001622, A019845, A019863.
Sequence in context: A287632 A259346 A239798 * A269557 A201581 A164597
Adjacent sequences: A019824 A019825 A019826 * A019828 A019829 A019830


KEYWORD

nonn,cons,easy


AUTHOR

N. J. A. Sloane


STATUS

approved



