A019851 - OEIS

A019851

Decimal expansion of sine of 42 degrees.

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

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OFFSET

0,1

COMMENTS

This sequence is also decimal expansion of cosine of 48 degrees. - Mohammad K. Azarian, Jun 29 2013

A quartic number with denominator 2. - Charles R Greathouse IV, Nov 05 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(4*Pi/15) = (sqrt(5) - 1)*(sqrt(3)*sqrt(5 + 2*sqrt(5)) - 1)/8 = 8*A019887^4 - 8*A019887^2 + 1 = sqrt(1 - A019857^2). - R. J. Mathar, Jun 18 2006

Equals 2*A019830*A019878. - R. J. Mathar, Jan 17 2021

A root of 16*x^4 - 8*x^3 - 16*x^2 + 8*x + 1 = 0. - R. J. Mathar, Aug 31 2025

EXAMPLE

0.6691306063588582138262733306867804735995832...

MATHEMATICA

First[RealDigits[Sin[42 Degree], 10, 100]] (* Paolo Xausa, Nov 15 2025 *)

PROG

(PARI) sin(7/30*Pi) \\ Charles R Greathouse IV, Nov 05 2017

CROSSREFS

Cf. A019857, A019887, A019830, A019878.

Sequence in context: A157320 A393652 A200616 * A155880 A393648 A389990

Adjacent sequences: A019848 A019849 A019850 * A019852 A019853 A019854

KEYWORD

nonn,cons,easy

AUTHOR

N. J. A. Sloane

STATUS

approved