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A272534 Decimal expansion of the edge length of a regular 15-gon with unit circumradius. 4
4, 1, 5, 8, 2, 3, 3, 8, 1, 6, 3, 5, 5, 1, 8, 6, 7, 4, 2, 0, 3, 4, 8, 4, 5, 6, 8, 8, 1, 0, 2, 5, 0, 3, 3, 2, 4, 3, 3, 1, 6, 9, 5, 2, 1, 2, 5, 5, 4, 4, 7, 6, 7, 2, 8, 1, 4, 3, 6, 3, 9, 4, 7, 7, 6, 4, 7, 6, 5, 6, 5, 1, 3, 2, 8, 1, 4, 8, 7, 5, 2, 6, 0, 9, 2, 5, 7, 5, 1, 3, 4, 4, 5, 4, 5, 5, 1, 4, 6, 1, 1, 5, 7, 3, 0 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

15-gon is the first m-gon with odd composite m which is constructible (see A003401) in virtue of the fact that 15 is the product of two distinct Fermat primes (A019434). The next such case is 51-gon (m=3*17), followed by 85-gon (m=5*17), 771-gon (m=3*257), etc.

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/m) for m=15.

Equals also (sqrt(3)-sqrt(15)+sqrt(10+2*sqrt(5)))/4.

EXAMPLE

0.415823381635518674203484568810250332433169521255447672814363947...

MATHEMATICA

RealDigits[N[2Sin[Pi/15], 100]][[1]] (* Robert Price, May 02 2016*)

PROG

(PARI) 2*sin(Pi/15)

CROSSREFS

Cf. A003401, A019434.

Edge lengths of other constructible m-gons: A002194 (m=3), A002193 (4), A182007 (5), A101464 (8), A094214 (10), A101263 (12), A272535 (16), A228787 (17), A272536 (20).

Sequence in context: A133866 A242131 A177266 * A173386 A011443 A016687

Adjacent sequences:  A272531 A272532 A272533 * A272535 A272536 A272537

KEYWORD

nonn,cons,easy

AUTHOR

Stanislav Sykora, May 02 2016

STATUS

approved

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Last modified July 22 00:13 EDT 2017. Contains 289648 sequences.