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%I #50 Oct 30 2023 23:54:59
%S 3,2,4,6,9,7,9,6,0,3,7,1,7,4,6,7,0,6,1,0,5,0,0,0,9,7,6,8,0,0,8,4,7,9,
%T 6,2,1,2,6,4,5,4,9,4,6,1,7,9,2,8,0,4,2,1,0,7,3,1,0,9,8,8,7,8,1,9,3,7,
%U 0,7,3,0,4,9,1,2,9,7,4,5,6,9,1,5,1,8,8,5,0,1,4,6,5,3,1,7,0,7,4,3,3,3,4,1,1
%N Decimal expansion of 2 + 2*cos(2*Pi/7).
%C A root of the equation x^3 - 5*x^2 + 6*x - 1 = 0. - _Arkadiusz Wesolowski_, Jan 13 2016
%C The other two roots of this minimal polynomial of the present algebraic number (rho(7))^2, with rho(7) = 2*cos(Pi/7) = A160389 are (2*cos(3*Pi/7))^2 = (A255241)^2 and (2*cos(5*Pi/7))^2 = (-A255249)^2. - _Wolfdieter Lang_, Mar 30 2020
%D Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 5.25 Tutte-Beraha Constants, p. 417.
%H Jesús Salas and Alan D. Sokal, <a href="https://arxiv.org/abs/cond-mat/0004330">Transfer matrices and partition functions zeros for antiferromagnetic Potts models</a>, arXiv:cond-mat/0004330 [cond-mat.stat-mech], 2000-2001, p. 64.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/LogisticMap.html">Logistic Map</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/SilverConstant.html">Silver Constant</a>
%H <a href="/index/Al#algebraic_03">Index entries for algebraic numbers, degree 3</a>
%F Equals (2*cos(Pi/7))^2 = (A160389)^2.
%F Equals 2 + i^(4/7) - i^(10/7). - _Peter Luschny_, Apr 04 2020
%e 3.246979603717467061...
%t First@ RealDigits[N[2 + 2 Cos[2 Pi/7], 120]] (* _Michael De Vlieger_, Jan 13 2016 *)
%o (PARI) 2 + 2*cos(2*Pi/7) \\ _Michel Marcus_, Jan 13 2016
%Y Cf. A231187, A160389.
%Y Cf. A003558, A054142, A255241, A255249.
%K nonn,cons,easy
%O 1,1
%A _Eric W. Weisstein_, Feb 15 2006
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