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
FORMULA
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
KEYWORD
AUTHOR
R. J. Mathar, Mar 03 2012
STATUS
approved