OFFSET
1,1
COMMENTS
Also the decimal expansion of cotangent of 18 degrees. - Mohammad K. Azarian, Jun 30 2013
A quartic integer. - Charles R Greathouse IV, Aug 27 2017
Length of the second longest diagonal in a regular 10-gon with unit side. - Mohammed Yaseen, Nov 12 2020
LINKS
Ivan Panchenko, Table of n, a(n) for n = 1..1000
Wikipedia, Exact trigonometric constants.
FORMULA
Equals sqrt(5 + 2*sqrt(5)). - R. J. Mathar, Jun 18 2006
Equals tan(66 degrees) + tan(36 degrees) + tan(6 degrees). - Amiram Eldar, Apr 07 2022
EXAMPLE
3.077683537175253402570290576036909824006702143537792427...
MATHEMATICA
RealDigits[Tan[72 Degree], 10, 120][[1]] (* Harvey P. Dale, Apr 30 2012 *)
RealDigitis[Sqrt[5 + 2*Sqrt[5]], 10, 100][[1]] (* G. C. Greubel, Nov 21 2018 *)
PROG
(PARI) tan(2*Pi/5) \\ Charles R Greathouse IV, Aug 27 2017
(Magma) SetDefaultRealField(RealField(100)); Sqrt(5+2*Sqrt(5)); // G. C. Greubel, Nov 21 2018
(Sage) numerical_approx(tan(2*pi/5), digits=100) # G. C. Greubel, Nov 21 2018
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
STATUS
approved