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A272536
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Decimal expansion of the edge length of a regular 20-gon with unit circumradius.
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4
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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
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OFFSET
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0,1
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COMMENTS
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Since 20-gon is constructible (see A003401), this is a constructible number.
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LINKS
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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
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FORMULA
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Equals 2*sin(Pi/20) = 2*A019818.
Equals also (sqrt(2)+sqrt(10)-2*sqrt(5-sqrt(5)))/4.
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EXAMPLE
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0.3128689300804617380202106389343337846277997841713215801692826921...
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MATHEMATICA
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RealDigits[N[2Sin[Pi/20], 100]][[1]] (* Robert Price, May 02 2016*)
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PROG
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(PARI) 2*sin(Pi/20)
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CROSSREFS
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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
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KEYWORD
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nonn,cons,easy
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AUTHOR
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Stanislav Sykora, May 02 2016
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STATUS
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approved
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