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A019918 Decimal expansion of tangent of 20 degrees.

%I A019918 #27 Aug 31 2025 12:53:09
%S A019918 3,6,3,9,7,0,2,3,4,2,6,6,2,0,2,3,6,1,3,5,1,0,4,7,8,8,2,7,7,6,8,3,4,0,
%T A019918 4,3,8,9,0,4,7,1,7,8,3,7,5,3,7,3,8,1,1,4,1,9,5,6,1,2,9,8,8,7,1,3,0,7,
%U A019918 3,9,6,2,1,0,0,4,8,9,6,3,8,8,2,4,3,8,5,4,5,7,4,0,3,1,4,6,3,8,5
%N A019918 Decimal expansion of tangent of 20 degrees.
%C A019918 Also the decimal expansion of cotangent of 70 degrees. - _Mohammad K. Azarian_, Jun 30 2013
%H A019918 Ivan Panchenko, <a href="/A019918/b019918.txt">Table of n, a(n) for n = 0..1000</a>
%H A019918 <a href="/index/Al#algebraic_06">Index entries for algebraic numbers, degree 6</a>.
%F A019918 Equals tan(Pi/9) = A019829/A019879. - _Bernard Schott_, Apr 19 2022
%F A019918 Smallest positive of the 6 real roots of x^6-33*x^4+27*x^2-3=0. (Other A019978, A019938). - _R. J. Mathar_, Aug 31 2025
%e A019918 0.36397023426620236135104788277683404389047...
%p A019918 evalf(tan(Pi/9), 100); # _Bernard Schott_, Apr 19 2022
%t A019918 First[RealDigits[Tan[Pi/9], 10, 100]] (* _Paolo Xausa_, Aug 01 2024 *)
%o A019918 (PARI) tan(Pi/9) \\ _Charles R Greathouse IV_, Feb 05 2025
%o A019918 (PARI) polrootsreal(x^6-33*x^4+27*x^2-3)[4] \\ _Charles R Greathouse IV_, Feb 05 2025
%Y A019918 Cf. A019938 (tan(2*Pi/9)).
%K A019918 nonn,cons,changed
%O A019918 0,1
%A A019918 _N. J. A. Sloane_