A102208 Decimal expansion of the volume of an icosahedron with unit edge length.

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

Offset

1,1

References

Jan Gullberg, Mathematics from the Birth of Numbers, W. W. Norton & Co., NY & London, 1997, §12.4 Theorems and Formulas (Solid Geometry), p. 451.

Links

Ivan Panchenko, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Icosahedron.

Wikipedia, Icosahedron - Area and volume.

Index entries for algebraic numbers, degree 2.

Formula

Equals 5 * (3 + sqrt(5))/12.

Equals 5*phi^2/6, phi being the golden ratio. - Stanislav Sykora, Nov 23 2013

Example

2.181694990624912373503822...

Mathematica

RealDigits[5/12*(3+Sqrt[5]), 10, 200][[1]] (* Vladimir Joseph Stephan Orlovsky, Feb 21 2011 *)

Prog

(PARI) 5*(3 + sqrt(5))/12 \\ G. C. Greubel, Jul 06 2017

Crossrefs

Cf. A001622 (phi), A020829 (regular tetrahedron volume), A131594 (regular octahedron volume), A102769 (regular dodecahedron volume).

Cf. A071402.

Sequence in context: A284346 A318651 A083529 * A371650 A369779 A379637

Adjacent sequences: A102205 A102206 A102207 * A102209 A102210 A102211

Keyword

cons,easy,nonn,changed

Author

Bryan Jacobs (bryanjj(AT)gmail.com), Feb 17 2005

Status

approved