OFFSET
1,1
COMMENTS
Equivalently, the area in the complex plane of the smallest convex set containing all order-5 roots of unity.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10001
Eric Weisstein et al., Root of Unity.
Eric Weisstein's World of Mathematics, de Moivre Number.
FORMULA
Equals (5*sqrt((5 + sqrt(5))/2))/4.
EXAMPLE
2.377641290737883930291098333448455358514246585314375556118264111075382925212...
MATHEMATICA
Floor[n/2]*Sin[(2*Pi)/n] - Sin[(4*Pi*Floor[n/2])/n]/2 /. n -> 5
RealDigits[(5(Sqrt[(5+Sqrt[5])/2]))/4, 10, 120][[1]] (* Harvey P. Dale, Jul 21 2013 *)
PROG
(PARI) (5*sqrt((5 + sqrt(5))/2))/4 \\ Michel Marcus, Feb 24 2023
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Joseph Biberstine (jrbibers(AT)indiana.edu), Mar 30 2005
STATUS
approved