A019970 Decimal expansion of tangent of 72 degrees.

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

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.

Index entries for algebraic numbers, degree 4

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

Cf. A019881 (sine of 72 degrees).

Cf. A019904, A019934, A019964.

Sequence in context: A316554 A201900 A344387 * A342698 A239022 A343612

Adjacent sequences: A019967 A019968 A019969 * A019971 A019972 A019973

Keyword

nonn,cons

Author

N. J. A. Sloane

Status

approved