A387447 Decimal expansion of cos(Pi/27).

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

Offset

0,1

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 9

Formula

Equals sin(25*Pi/54) = 2F1(-1/18,1/18;1/2;3/4).

Largest of the 9 real-valued roots of 512*x^9 -1152*x^7 +864*x^5 -240*x^3 +18*x -1 =0.

4*this^3 -3*this = A019879.

Example

0.99323835774194298854789555219370434034910619707069...

Mathematica

First[RealDigits[Cos[Pi/27], 10, 100]] (* Paolo Xausa, Nov 17 2025 *)

Crossrefs

Sequence in context: A011211 A074879 A397227 * A291366 A146490 A222810

Adjacent sequences: A387444 A387445 A387446 * A387448 A387449 A387450

Keyword

nonn,cons,easy

Author

R. J. Mathar, Aug 29 2025

Status

approved