A236367 Dihedral angle in a regular icosahedron (radians).

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, 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, 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

Offset: 1

Author

Stanislav Sykora, Jan 23 2014

Keywords

• nonn
• cons
• easy

Examples

			2.41186499736282687500784672346618218880066348532739213...
		

Links

• Stanislav Sykora, Table of n, a(n) for n = 1..2000
• Wikipedia, Platonic solid.

Crossrefs

Cf. A001622, Platonic solids dihedral angles: A137914 (tetrahedron), A156546 (octahedron), A019669 (cube), A137218 (dodecahedron).

Programs

Mathematica

RealDigits[2 * ArcTan[GoldenRatio^2], 10, 120][[1]] (* Amiram Eldar, May 17 2023 *)

PARI

2*atan((3+sqrt(5))/2)

Formula

Equals 2*arctan(phi^2) = 2*arctan(A001622^2) = 2*arctan((3+sqrt(5))/2).