A272536 Decimal expansion of the edge length of a regular 20-gon with unit circumradius.

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

Offset

0,1

Comments

Since 20-gon is constructible (see A003401), this is a constructible number.

Links

Stanislav Sykora, Table of n, a(n) for n = 0..2000

Mauro Fiorentini, Construibili (numeri)

Eric Weisstein's World of Mathematics, Constructible Number

Wikipedia, Constructible number

Wikipedia, Regular polygon

Formula

Equals 2*sin(Pi/20) = 2*A019818.

Equals also (sqrt(2)+sqrt(10)-2*sqrt(5-sqrt(5)))/4.

Equals i^(9/10) + i^(-9/10). - Gary W. Adamson, Jul 08 2022

Example

0.3128689300804617380202106389343337846277997841713215801692826921...

Mathematica

RealDigits[N[2Sin[Pi/20], 100]][[1]] (* Robert Price, May 02 2016*)

Prog

(PARI) 2*sin(Pi/20)

Crossrefs

Cf. A003401.

Edge lengths of other constructible m-gons: A002194 (m=3), A002193 (4), A182007 (5), A101464 (8), A094214 (10), A101263 (12), A272534 (15), A272535 (16), A228787 (17).

Cf. A019818.

Sequence in context: A204128 A266272 A201677 * A204122 A201657 A279384

Adjacent sequences: A272533 A272534 A272535 * A272537 A272538 A272539

Keyword

nonn,cons,easy

Author

Stanislav Sykora, May 02 2016

Status

approved