A256853 Decimal expansion of area of a regular 9-gon with unit edge length.

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

Offset

1,1

Links

Stanislav Sykora, Table of n, a(n) for n = 1..2000

Wikipedia, Nonagon

Wikipedia, Regular polygon

Index entries for algebraic numbers, degree 6

Formula

Equals (p/4)*cot(Pi/p), with p = 9.

Example

6.181824193772900127213744059619763614941713348134358098386864...

Mathematica

RealDigits[(9/4)*Cot[Pi/9], 10, 50][[1]] (* G. C. Greubel, Jul 03 2017 *)

Prog

(PARI) p=9; a=(p/4)*cotan(Pi/p)        \\ Use realprecision in excess

Crossrefs

Cf. A000796, A019968, A120011 (p=3), A102771 (p=5), A104956 (p=6), A178817 (p=7), A090488 (p=8), A178816 (p=10), A256854 (p=11), A178809 (p=12).

Sequence in context: A186099 A021622 A073228 * A349905 A258404 A244692

Adjacent sequences: A256850 A256851 A256852 * A256854 A256855 A256856

Keyword

nonn,cons

Author

Stanislav Sykora, Apr 12 2015

Status

approved