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%I #8 Nov 22 2024 11:07:25
%S 2,2,6,0,5,7,1,3,2,7,5,8,0,3,9,6,2,7,9,3,4,1,3,5,7,8,1,1,6,0,8,6,5,5,
%T 9,6,5,5,5,5,2,8,4,1,8,0,5,3,8,1,2,6,2,4,1,4,3,2,0,8,6,9,2,9,0,2,4,3,
%U 4,2,7,6,4,6,3,1,4,2,4,7,7,2,1,0,8,6,3,9,2,3
%N Decimal expansion of the dihedral angle, in radians, between any two adjacent faces in a triakis tetrahedron.
%C The triakis tetrahedron is the dual polyhedron of the truncated tetrahedron.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Triakis_tetrahedron">Triakis tetrahedron</a>.
%F Equals arccos(-7/11).
%e 2.2605713275803962793413578116086559655552841805381...
%t First[RealDigits[ArcCos[-7/11], 10, 100]] (* or *)
%t First[RealDigits[First[PolyhedronData["TriakisTetrahedron", "DihedralAngles"]], 10, 100]]
%Y Cf. A378204 (surface area), A378205 (volume), A378206 (inradius), A378207 (midradius).
%Y Cf. A137914 and A156546 (dihedral angles of a truncated tetrahedron).
%K nonn,cons,easy
%O 1,1
%A _Paolo Xausa_, Nov 21 2024