OFFSET
0,1
COMMENTS
Cubic number with denominator 2 and minimal polynomial 8*x^3 - 4*x^2 - 4*x + 1. - Charles R Greathouse IV, May 13 2019
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..10000
Kevin S. Brown's MathPages, Radical Expression For cos(2*Pi/7)
FORMULA
Equals Hypergeometric2F1([5/7, 2/7], [1/2], 3/4)/2 . - R. J. Mathar, Oct 27 2008
Equals (1/6)*(1 + (7*(-1 +3*sqrt(3)*I)/2)^(1/3) + (-7*(1 +3*sqrt(3)*I)/2)^(1/3)). - G. C. Greubel, Sep 04 2022
EXAMPLE
Cos(Pi/7) = 0.90096886790241912623610231950744505116139...
MATHEMATICA
RealDigits[ Cos[Pi/7], 10, 105] [[1]]
PROG
(PARI) cos(Pi/7) \\ Charles R Greathouse IV, May 13 2019
(Magma) R:= RealField(120); Cos(Pi(R)/7); // G. C. Greubel, Sep 04 2022
(SageMath) numerical_approx(cos(pi/7), digits=120) # G. C. Greubel, Sep 04 2022
CROSSREFS
KEYWORD
cons,nonn
AUTHOR
Robert G. Wilson v, Aug 15 2002
STATUS
approved