A019907 Decimal expansion of tangent of 9 degrees.

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

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• cons
• changed

Comments

Also the decimal expansion of cotangent of 81 degrees. - Mohammad K. Azarian, Jun 30 2013

Links

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

Programs

Mathematica

RealDigits[Tan[9 Degree],10,120][[1]] (* Harvey P. Dale, Aug 23 2020 *)

Formula

Equals tan(Pi/20) = A019818/A019890. - R. J. Mathar, Aug 29 2025

Smallest positive of the 8 real-valued roots of x^8-44*x^6+166*x^4-44*x^2+1=0. (Others A019925, A019961, A019979). - R. J. Mathar, Aug 31 2025