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A019694 Decimal expansion of 2*Pi/5. 26
1, 2, 5, 6, 6, 3, 7, 0, 6, 1, 4, 3, 5, 9, 1, 7, 2, 9, 5, 3, 8, 5, 0, 5, 7, 3, 5, 3, 3, 1, 1, 8, 0, 1, 1, 5, 3, 6, 7, 8, 8, 6, 7, 7, 5, 9, 7, 5, 0, 0, 4, 2, 3, 2, 8, 3, 8, 9, 9, 7, 7, 8, 3, 6, 9, 2, 3, 1, 2, 6, 5, 6, 2, 5, 1, 4, 4, 8, 3, 5, 9, 9, 4, 5, 1, 2, 1, 3, 9, 3, 0, 1, 3, 6, 8, 4, 6, 8, 2 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also, with proper offset, decimal expansion of the magnetic permeability of vacuum in SI units, mu_0 = 4*Pi*10^-7 N A^-2, an assigned metrological constant.

Regarding these, see A003678 for general context notes, references and links. - Stanislav Sykora, Jun 16 2012

Iff n is +- 1, 2, 3, 4 or 6, then 2*cos(2*Pi/n) is an integer. This formula plays a role in the short proof of the Crystallographic Restriction Theorem (see A217290). For n = 5, 2*cos(2*Pi/5) = 1/Golden Ratio = 0.6180339887..., associated with quasicrystals and 5-fold rotational symmetry. - Raphie Frank, Dec 21 2012

With offset 2 this is also the decimal expansion of 4*Pi, the surface area of a sphere whose diameter equals the square root of 4, hence its radius is 1. More generally x*Pi is also the surface area of a sphere whose diameter equals the square root of x. - Omar E. Pol, Jan 18 2013, Oct 05 2013, Dec 22 2013

LINKS

Ivan Panchenko, Table of n, a(n) for n = 1..1000

NIST, magnetic constant mu_0.

Nobelprize.org, The Discovery of Quasicrystals (PDF).

Wikipedia, Crystallographic Restriction Theorem.

EXAMPLE

1.2566370614359172953850573533118... - Vladimir Joseph Stephan Orlovsky, Dec 02 2009

mu_0 = 12.566370614359172953850573533118... 10^-7 N/A^2. - Stanislav Sykora, Jun 16 2012

MAPLE

Digits:=100: evalf(2*Pi/5); # Wesley Ivan Hurt, Jan 07 2017

MATHEMATICA

RealDigits[ 2*Pi/5, 10, 111][[1]] (* Vladimir Joseph Stephan Orlovsky, Dec 02 2009 and modified by Robert G. Wilson v *)

PROG

(PARI) 2*Pi/5 \\ G. C. Greubel, Sep 11 2017

CROSSREFS

Other assigned constants: A003678, A072915, A081799, A182999, A213610, A213611, A213612, A213613, A213614.

Sequence in context: A272207 A155947 A008294 * A233588 A113975 A035585

Adjacent sequences:  A019691 A019692 A019693 * A019695 A019696 A019697

KEYWORD

nonn,cons,changed

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified September 25 05:48 EDT 2017. Contains 292442 sequences.