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A102771
Decimal expansion of area of a regular pentagon with unit edge length.
15
1, 7, 2, 0, 4, 7, 7, 4, 0, 0, 5, 8, 8, 9, 6, 6, 9, 2, 2, 7, 5, 9, 0, 1, 1, 9, 7, 7, 3, 8, 8, 6, 0, 9, 5, 9, 9, 4, 0, 7, 3, 7, 4, 1, 7, 0, 0, 1, 0, 1, 9, 8, 3, 2, 9, 2, 0, 7, 0, 9, 4, 7, 0, 7, 0, 2, 3, 8, 6, 8, 9, 9, 2, 2, 0, 8, 9, 6, 6, 2, 3, 1, 3, 3, 2, 4, 4, 1, 2, 4, 1, 3, 8, 7, 5, 8, 7, 7, 4
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Pentagon
FORMULA
Equals sqrt(25 + 10*sqrt(5)) / 4.
Equals (3*phi+1)*sqrt(3-phi) with the golden section phi = (1 + sqrt(5))/2. - Wolfdieter Lang, Jan 25 2013
Equals 5/(4*tan(Pi/5)). - Michel Marcus, Mar 25 2015
Equals (5/4)*sqrt(phi^3/sqrt(5)). - G. C. Greubel, Jul 03 2017
EXAMPLE
1.720477400588966922759011977...
MATHEMATICA
RealDigits[(5/4)*Sqrt[GoldenRatio^3/Sqrt[5]], 10, 50][[1]] (* G. C. Greubel, Jul 03 2017 *)
PROG
(PARI) 5/(4*tan(Pi/5)) \\ Michel Marcus, Mar 25 2015
CROSSREFS
Cf. Areas of other regular polygons: A120011, A104956, A178817, A090488, A256853, A178816, A256854, A178809.
Sequence in context: A258753 A248363 A220674 * A341798 A232812 A245740
KEYWORD
nonn,cons
AUTHOR
Bryan Jacobs (bryanjj(AT)gmail.com), Feb 10 2005
EXTENSIONS
Corrected the title. - Stanislav Sykora, Apr 12 2015
STATUS
approved