A391657 - OEIS

%I #11 Dec 16 2025 09:32:29

%S 2,0,0,3,6,5,7,1,9,4,9,7,7,0,5,8,5,4,3,0,8,3,1,9,8,4,4,2,6,4,3,0,4,6,

%T 4,8,8,3,5,9,0,0,3,0,4,4,0,0,8,2,9,2,1,4,3,3,7,0,2,2,5,7,6,0,0,3,2,9,

%U 7,7,3,1,1,6,2,5,0,7,5,8,2,5,3,1,1,9,3,5,2,3

%N Decimal expansion of the dihedral angle, in radians, between a pentagonal face and a triangular face in a Dürer's solid.

%C The value of this constant is based on the interpretation of Dürer's solid given in A391653. See there for more information and links.

%H Paolo Xausa, <a href="/A391657/b391657.txt">Table of n, a(n) for n = 1..10000</a>

%F Equals arccos(-sqrt((5 - 2*sqrt(5))/3)) = arccos(-sqrt((5 - A010476)/3)).

%e 2.003657194977058543083198442643046488359003044008...

%t First[RealDigits[ArcCos[-Sqrt[(5 - Sqrt[20])/3]], 10, 100]] (* or *)

%t First[RealDigits[Max[PolyhedronData["DuererSolid", "DihedralAngles"]], 10, 100]]

%Y Cf. other dihedral angles: A238238, A391656.

%Y Cf. A391653 (volume), A391654 (surface area), A391655 (circumradius).

%Y Cf. A080992, A010476.

%K nonn,cons,easy

%O 1,1

%A _Paolo Xausa_, Dec 16 2025