A208899 Decimal expansion of sqrt(5)/3.

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

Offset

0,1

Comments

Equals the absolute value of the cosine of the dihedral angle between two adjacent faces of the regular icosahedron.

Links

Ivan Panchenko, Table of n, a(n) for n = 0..1000

Mathematics Stack Exchange, Maximum and Minimum Value of f(x)

Michael Penn, an "extreme" extreme value problem., YouTube video, 2022.

Wikipedia, Exsphere

Index entries for algebraic numbers, degree 2.

Formula

Equals A002163/3 = 20*A020837/3.

Equals Sum_{k>=0} (-1)^k * binomial(2*k,k)/5^k. - Amiram Eldar, Aug 03 2020

Example

0.7453559924...

Mathematica

RealDigits[Sqrt[5]/3, 10, 120][[1]] (* Harvey P. Dale, Jul 03 2013 *)

Prog

(PARI) first(n) = default(realprecision, max(28, n+10)); digits(((sqrt(5)/3)*10^n)\1) \\ David A. Corneth, Dec 19 2022

Crossrefs

Cf. A002163, A020837.

Sequence in context: A011475 A180078 A019685 * A393630 A087491 A019899

Adjacent sequences: A208896 A208897 A208898 * A208900 A208901 A208902

Keyword

nonn,cons,easy

Author

R. J. Mathar, Mar 03 2012

Status

approved