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A019970
Decimal expansion of tangent of 72 degrees.
11
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
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).
Sequence in context: A316554 A201900 A344387 * A342698 A239022 A343612
KEYWORD
nonn,cons
STATUS
approved