A387440 Decimal expansion of cos(Pi/11).

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

Offset

0,1

Comments

The 11th cyclotomic polynomial is 1+x+x^2+x^3+..+x^10 and has the roots -this+-0.28173255..*i, -0.65486073.. +- 0.7557495..*i, -0.142314838... +- A387443*i, 0.415415013 +- 0.909631995..*i, 0.841253532.. +- 0.540640817..*i. - R. J. Mathar, Jun 11 2026

Links

Paolo Xausa, Table of n, a(n) for n = 0..10000

R. J. Mathar, Reduction formulas of the cosine of integer fractions of pi, (2008) vixra:2210.0026.

Index entries for algebraic numbers, degree 5.

Formula

Largest of the 5 real-valued roots of 32*x^5 -16*x^4 -32*x^3 +12*x^2 +6*x-1 =0.

Equals sin(9*Pi/22).

Example

0.95949297361449738989036805706632769906245484842216...

Mathematica

First[RealDigits[Cos[Pi/11], 10, 100]] (* Paolo Xausa, Nov 18 2025 *)

Crossrefs

Cf. A019678.

Sequence in context: A154830 A201284 A191815 * A341430 A341438 A265290

Adjacent sequences: A387437 A387438 A387439 * A387441 A387442 A387443

Keyword

nonn,cons,easy

Author

R. J. Mathar, Aug 29 2025

Status

approved