login
A232812
Decimal expansion of the surface index of a regular tetrahedron.
10
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
OFFSET
1,1
COMMENTS
Equivalently, the surface area of a regular tetrahedron 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).
FORMULA
Equals 2*sqrt(3)*3^(2/3).
Equals A002194/A020829^(2/3).
EXAMPLE
7.20562173105601636005279232409725707779044450935589335...
MATHEMATICA
RealDigits[2*Sqrt[3]*3^(2/3), 10, 120][[1]] (* Amiram Eldar, May 25 2023 *)
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: A220674 A102771 A341798 * A245740 A318922 A236565
KEYWORD
nonn,cons,easy
AUTHOR
Stanislav Sykora, Dec 01 2013
STATUS
approved