A019964 -id:A019964 - cp's OEIS frontend

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

N. J. A. Sloane

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

			tan(2*Pi/5) = 3.077683537175253402570290576036909824006702143537792427...

Ivan Panchenko, Table of n, a(n) for n = 1..1000
Wikipedia, Exact trigonometric constants.
Index entries for algebraic numbers, degree 4

Cf. A019881 (sine of 72 degrees).

Cf. A019904, A019934, A019964.

SetDefaultRealField(RealField(100)); Sqrt(5+2*Sqrt(5)); // G. C. Greubel, Nov 21 2018

RealDigits[Tan[72 Degree],10,120][[1]] (* Harvey P. Dale, Apr 30 2012 *)
RealDigits[Sqrt[5 + 2*Sqrt[5]], 10, 100][[1]] (* G. C. Greubel, Nov 21 2018 *)

tan(2*Pi/5) \\ Charles R Greathouse IV, Aug 27 2017

numerical_approx(tan(2*pi/5), digits=100) # G. C. Greubel, Nov 21 2018

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
Largest positive of the 4 real-valued roots of x^4-10*x^2+5=0. - R. J. Mathar, Aug 31 2025
Equals A019881/A019827. - R. J. Mathar, Sep 05 2025

A019904 Decimal expansion of tangent of 6 degrees.

Original entry on oeis.org

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

Offset: 0

N. J. A. Sloane

Also the decimal expansion of cotangent of 84 degrees. - Mohammad K. Azarian, Jun 30 2013
An algebraic integer of degree 8. - Charles R Greathouse IV, Nov 17 2017
Root of the polynomial 1-92*x^2+134*x^4-28*x^6+x^8=0. (Others: A019940, A019964, A019976). - R. J. Mathar, Sep 06 2025

			tan(Pi/30) = 0.105104235...

Ivan Panchenko, Table of n, a(n) for n = 0..1000
Wikipedia, Exact trigonometric constants
Index entries for algebraic numbers, degree 8

RealDigits[Tan[6 Degree],10,120][[1]] (* Harvey P. Dale, Jun 18 2024 *)

tan(Pi/30) \\ Charles R Greathouse IV, Nov 17 2017

Equals A019815 / A019839 = A019821/(1+A019887). - R. J. Mathar, Sep 06 2025

cp's OEIS Frontend

A019970 Decimal expansion of tangent of 72 degrees.

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