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A255249 Decimal expansion of -2 cos(5 Pi/7). 1
1, 2, 4, 6, 9, 7, 9, 6, 0, 3, 7, 1, 7, 4, 6, 7, 0, 6, 1, 0, 5, 0, 0, 0, 9, 7, 6, 8, 0, 0, 8, 4, 7, 9, 6, 2, 1, 2, 6, 4, 5, 4, 9, 4, 6, 1, 7, 9, 2, 8, 0, 4, 2, 1, 0, 7, 3, 1, 0, 9, 8, 8, 7, 8, 1, 9, 3, 7, 0, 7, 3, 0, 4, 9, 1, 2, 9, 7, 4, 5, 6, 9, 1, 5, 1, 8, 8, 5, 0, 1, 4, 6, 5, 3, 1, 7, 0 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

rho_3 := +2*cos(5*Pi/5) is the negative zero of the minimal polynomial C(7, x) = x^3 - x^2 - 2*x + 1 of the algebraic number rho(7) = 2*cos(Pi/7), the length ratio of the smaller diagonal and the side in the regular 7-gon (heptagon). See A187360 and a link to the arXiv paper given there, eq. (20) for the zeros of C(n, x). The positive zeros are rho(7) and rho_2 = 2*cos(3*Pi/7) shown in A160389 and A255241.

Essentially the same as A231187 and A116425. - R. J. Mathar, Mar 14 2015

LINKS

Table of n, a(n) for n=1..97.

FORMULA

2*cos(5*Pi/7) = - 2*sin(3*Pi/14) = -1.246979603...

CROSSREFS

Cf. A160389, A255241, A187360.

Sequence in context: A283501 A248761 A176461 * A084407 A114526 A178126

Adjacent sequences:  A255246 A255247 A255248 * A255250 A255251 A255252

KEYWORD

nonn,cons

AUTHOR

Wolfdieter Lang, Mar 13 2015

STATUS

approved

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Last modified August 20 10:17 EDT 2019. Contains 326149 sequences. (Running on oeis4.)