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A019827 Decimal expansion of sine of 18 degrees. 11
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 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Decimal expansion of cosine of 72 degrees.

If the offset is changed to 1, the constant is 3.090169.. = 5/A001622. - Omar E. Pol, Nov 15 2007

Also the imaginary part of i^(1/5). - Stanislav Sykora, Apr 25 2012

One of two roots of 4x^2 + 2x - 1 (the other is the sine of 54 degrees times -1). - Alonso del Arte, Apr 25 2015

LINKS

Zak Seidov, Table of n, a(n) for n = 0..999

Wikipedia, Exact trigonometric constants

FORMULA

Equals (sqrt(5) - 1)/4.

Equals 1/(1 + sqrt(5)). - Omar E. Pol, Nov 15 2007

EXAMPLE

(sqrt(5) - 1)/4 = 0.309016994374947424102293417182819...

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. A019845 (sine of 36 degrees), A019863 (sine of 54 degrees).

Sequence in context: A068607 A167004 A239798 * A201581 A164597 A167295

Adjacent sequences:  A019824 A019825 A019826 * A019828 A019829 A019830

KEYWORD

nonn,cons,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified May 22 17:58 EDT 2015. Contains 257746 sequences.