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%I #15 May 17 2023 08:41:22
%S 2,4,1,1,8,6,4,9,9,7,3,6,2,8,2,6,8,7,5,0,0,7,8,4,6,7,2,3,4,6,6,1,8,2,
%T 1,8,8,8,0,0,6,6,3,4,8,5,3,2,7,3,9,2,1,3,0,2,6,5,9,9,5,1,0,0,8,4,5,9,
%U 9,7,5,0,6,6,1,9,4,4,1,8,5,9,8,3,2,5,5,1,4,1,7,5,2,2,6,4,3,5,6,7,7,7,4,0,5
%N Dihedral angle in a regular icosahedron (radians).
%H Stanislav Sykora, <a href="/A236367/b236367.txt">Table of n, a(n) for n = 1..2000</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Platonic_solid">Platonic solid</a>.
%F Equals 2*arctan(phi^2) = 2*arctan(A001622^2) = 2*arctan((3+sqrt(5))/2).
%e 2.41186499736282687500784672346618218880066348532739213...
%t RealDigits[2 * ArcTan[GoldenRatio^2], 10, 120][[1]] (* _Amiram Eldar_, May 17 2023 *)
%o (PARI) 2*atan((3+sqrt(5))/2)
%Y Cf. A001622, Platonic solids dihedral angles: A137914 (tetrahedron), A156546 (octahedron), A019669 (cube), A137218 (dodecahedron).
%K nonn,cons,easy
%O 1,1
%A _Stanislav Sykora_, Jan 23 2014
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