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A232812 Decimal expansion of the surface index of a regular tetrahedron. 9
7, 2, 0, 5, 6, 2, 1, 7, 3, 1, 0, 5, 6, 0, 1, 6, 3, 6, 0, 0, 5, 2, 7, 9, 2, 3, 2, 4, 0, 9, 7, 2, 5, 7, 0, 7, 7, 7, 9, 0, 4, 4, 4, 5, 0, 9, 3, 5, 5, 8, 9, 3, 3, 5, 0, 1, 1, 0, 2, 2, 8, 3, 4, 2, 6, 9, 5, 2, 3, 3, 6, 2, 4, 1, 1, 4, 5, 6, 7, 5, 1, 6, 2, 6, 8, 4, 5, 0, 7, 3, 0, 2, 1, 8, 5, 2, 1, 5, 7, 8, 6, 0, 9, 1, 7 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Equivalently, the surface area of a regular octahedron with unit volume. Among Platonic solids, surface indices decrease with increasing number of faces: this one, 6.0 (cube = hexahedron), A232811 (octahedron), A232810 (dodecahedron), and A232809 (icosahedron).

LINKS

Stanislav Sykora, Table of n, a(n) for n = 1..1000

Wikipedia, Platonic solid

FORMULA

2*sqrt(3)*3^(2/3).

A002194/A020829^(2/3).

EXAMPLE

7.20562173105601636005279232409725707779044450935589335...

PROG

(PARI) sqrtn(139968, 6) \\ Charles R Greathouse IV, Apr 25 2016

CROSSREFS

Cf. A002194, A020829, A232808 (surface index of a sphere), A232809, A232810, A232811.

Sequence in context: A248363 A220674 A102771 * A245740 A236565 A093954

Adjacent sequences:  A232809 A232810 A232811 * A232813 A232814 A232815

KEYWORD

nonn,cons,easy

AUTHOR

Stanislav Sykora, Dec 01 2013

STATUS

approved

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Last modified August 19 19:25 EDT 2017. Contains 290821 sequences.