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A214549
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Decimal expansion of 4*Pi^2/27.
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10
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1, 4, 6, 2, 1, 6, 3, 6, 1, 4, 9, 7, 6, 2, 0, 1, 2, 7, 6, 8, 6, 4, 3, 6, 9, 0, 3, 7, 0, 1, 8, 6, 8, 9, 0, 5, 7, 0, 8, 3, 5, 1, 1, 0, 2, 3, 2, 9, 4, 9, 3, 1, 9, 4, 4, 6, 5, 3, 8, 2, 9, 5, 3, 7, 2, 1, 7, 7, 8, 4, 4, 1, 8, 1, 3, 6, 1, 7, 8, 5, 5, 4, 5, 1, 8, 7, 8, 1, 2, 4, 4, 9, 9
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OFFSET
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1,2
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COMMENTS
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Represents the value of the Dirichlet series for A011655 (principal Dirichlet character mod 3) at s=2.
Equals the asymptotic mean of the abundancy index of the numbers that are not divisible by 3 (A001651). - Amiram Eldar, May 12 2023
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LINKS
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FORMULA
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Equals Sum_{n>=0} (1/(3*n+1)^2 + 1/(3*n+2)^2).
Equals (8/9) * Sum_(k>=1) 1/k^2 =8/9 *A013661.
Equals -(16/9) * Sum_(k>=1) (-1)^k/k^2 = -16/9 * A072691.
Equals (64/27) * ( Integral_{x=0..1} sqrt(1 - x^2) )^2 = 64/27 * A091476. (End)
Equals Integral_{x=0..oo} log(x)/(x^3 - 1) dx. - Amiram Eldar, Aug 12 2020
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EXAMPLE
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1.4621636149762012768643690370186...
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MAPLE
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evalf(4*Pi^2/27) ;
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MATHEMATICA
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RealDigits[(4Pi^2)/27, 10, 120][[1]] (* Harvey P. Dale, Dec 20 2012 *)
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PROG
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(Magma) R:= RealField(); 4*Pi(R)^2/27; // G. C. Greubel, Mar 08 2018
(Magma) R:=RealField(106); SetDefaultRealField(R); n:=4*Pi(R)^2/27; Reverse(Intseq(Floor(10^105*n))); // Bruno Berselli, Mar 13 2018
(Julia)
using Nemo
R = RealField(310)
t = const_pi(RR) + const_pi(RR); s = t * t
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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