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%I #18 May 31 2021 03:24:19
%S 6,9,4,5,9,2,7,1,0,6,6,7,7,2,1,3,9,5,4,0,6,8,6,6,5,0,7,0,7,7,2,5,9,1,
%T 8,4,0,0,1,5,0,2,7,0,8,7,3,6,2,7,7,5,4,8,9,4,4,9,6,5,5,1,2,5,2,8,2,6,
%U 3,2,8,8,5,5,6,0,5,8,9,4,1,6,8,6,0,6,6,4,5,2,6,2,9,5,9,8,2,9,6,0,4,7,8,3,6
%N Decimal expansion of -2*cos((2*Pi)/9) + 2*sqrt(3)*sin((2*Pi)/9).
%C The distance between the centers of 2 unit-radius spheres such that the volume of the overlap is equal to half the volume of each sphere. - _Amiram Eldar_, May 31 2021
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Sphere-SphereIntersection.html">Sphere-Sphere Intersection</a>.
%F Equals 4*sin(Pi/18) = 4*A019819. - _Gleb Koloskov_, Feb 28 2021
%e 0.69459271066772139540...
%t RealDigits[-2*Cos[(2*Pi)/9] + 2*Sqrt[3]*Sin[(2*Pi)/9], 10, 100][[1]] (* _Vaclav Kotesovec_, Aug 16 2015 *)
%o (PARI) 4*sin(Pi/18) \\ _Gleb Koloskov_, Feb 28 2021
%Y Cf. A019819.
%K nonn,cons
%O 0,1
%A _Eric W. Weisstein_, Sep 23 2007
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