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%I #31 Aug 21 2023 11:16:45
%S 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,
%T 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,
%U 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
%N Decimal expansion of sine of 42 degrees.
%C This sequence is also decimal expansion of cosine of 48 degrees. - _Mohammad K. Azarian_, Jun 29 2013
%C A quartic number with denominator 2. - _Charles R Greathouse IV_, Nov 05 2017
%H Ivan Panchenko, <a href="/A019851/b019851.txt">Table of n, a(n) for n = 0..1000</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Exact_trigonometric_constants">Exact trigonometric constants</a>
%H <a href="/index/Al#algebraic_04">Index entries for algebraic numbers, degree 4</a>
%F 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
%F Equals 2*A019830*A019878. - _R. J. Mathar_, Jan 17 2021
%e 0.6691306...
%o (PARI) sin(7/30*Pi) \\ _Charles R Greathouse IV_, Nov 05 2017
%Y Cf. A019857, A019887, A019830, A019878.
%K nonn,cons
%O 0,1
%A _N. J. A. Sloane_
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