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 A065464 Decimal expansion of Product_{p prime}(1 - (2*p-1)/p^3). 17
 4, 2, 8, 2, 4, 9, 5, 0, 5, 6, 7, 7, 0, 9, 4, 4, 4, 0, 2, 1, 8, 7, 6, 5, 7, 0, 7, 5, 8, 1, 8, 2, 3, 5, 4, 6, 1, 2, 1, 2, 9, 8, 5, 1, 3, 3, 5, 5, 9, 3, 6, 1, 4, 4, 0, 3, 1, 9, 0, 1, 3, 7, 9, 5, 3, 2, 1, 2, 3, 0, 5, 2, 1, 6, 1, 0, 8, 3, 0, 4, 4, 1, 0, 5, 3, 4, 8, 5, 1, 4, 5, 2, 4, 6, 8, 0, 6, 8, 5, 5, 4, 8, 0, 7, 5, 7 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Sum_{n <= x} A189021(n) ~ kx, where k is this constant. - Charles R Greathouse IV, Jan 24 2018 The probability that a number chosen at random is squarefree and coprime to another randomly chosen random (see Schroeder, 2009). - Amiram Eldar, May 23 2020, corrected Aug 04 2020 REFERENCES Manfred Schroeder, Number Theory in Science and Communication, 5th edition, Springer, 2009, page 59. LINKS R. J. Mathar, Hardy-Littlewood Constants Embedded into Infinite Products over All Positive Integers, arXiv:0903.2514 [math.NT], 2009-2011; Equation (116). G. Niklasch, Some number theoretical constants: 1000-digit values. [Cached copy] Eric Weisstein's World of Mathematics, Carefree Couple. FORMULA Equals A065463 divided by A013661. - R. J. Mathar, Mar 22 2011 Equals A065473 divided by A065480. - R. J. Mathar, May 02 2019 Equals (6/Pi^2)^2 * Product_{p prime} (1 + 1/(p^3 + p^2 - p - 1)) = 1.1587609... * (6/Pi^2)^2. - Amiram Eldar, May 23 2020 Equals lim_{m->oo} (1/m) * Sum_{k==1..m} (phi(k)/k)^2, where phi is the Euler totient function (A000010). - Amiram Eldar, Mar 12 2021 EXAMPLE 0.428249505677094440218765707581823546... MATHEMATICA \$MaxExtraPrecision = 800; digits = 98; terms = 2000; LR = Join[{0, 0}, LinearRecurrence[{-2, 0, 1}, {-2, 3, -6}, terms+10]]; r[n_Integer] := LR[[n]]; (6/Pi^2)*Exp[NSum[r[n]*(PrimeZetaP[n-1]/(n-1)), {n, 3, terms}, NSumTerms -> terms, WorkingPrecision -> digits+10, Method -> "AlternatingSigns"]] // RealDigits[#, 10, digits]& // First (* Jean-François Alcover, Apr 16 2016 *) PROG (PARI) prodeulerrat(1 - (2*p-1)/p^3) \\ Amiram Eldar, Mar 12 2021 CROSSREFS Cf. A000010, A057434, A078078. Cf. A065463, A013661. Cf. A065473, A065480. Sequence in context: A112152 A211883 A083489 * A201400 A040015 A144926 Adjacent sequences:  A065461 A065462 A065463 * A065465 A065466 A065467 KEYWORD cons,nonn AUTHOR N. J. A. Sloane, Nov 19 2001 EXTENSIONS More digits from Vaclav Kotesovec, Dec 18 2019 STATUS approved

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Last modified December 7 13:08 EST 2021. Contains 349581 sequences. (Running on oeis4.)