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 A059956 Decimal expansion of 6/Pi^2. 33
 6, 0, 7, 9, 2, 7, 1, 0, 1, 8, 5, 4, 0, 2, 6, 6, 2, 8, 6, 6, 3, 2, 7, 6, 7, 7, 9, 2, 5, 8, 3, 6, 5, 8, 3, 3, 4, 2, 6, 1, 5, 2, 6, 4, 8, 0, 3, 3, 4, 7, 9, 2, 9, 3, 0, 7, 3, 6, 5, 4, 1, 9, 1, 3, 6, 5, 0, 3, 8, 7, 2, 5, 7, 7, 3, 4, 1, 2, 6, 4, 7, 1, 4, 7, 2, 5, 5, 6, 4, 3, 5, 5, 3, 7, 3, 1, 0, 2, 5, 6, 8, 1, 7, 3, 3 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS "6/Pi^2 is the probability that two randomly selected numbers will be coprime and also the probability that a randomly selected integer is 'squarefree.'" [Hardy and Wright] - C. Pickover. In fact, the probability that any k randomly selected numbers will be coprimes is 1/Sum_{n>=1} n^(-k) = 1/zeta(k). - Robert G. Wilson v [corrected by Ilya Gutkovskiy, Aug 18 2018] 6/Pi^2 is also the diameter of a circle whose circumference equals the ratio of volume of a cuboid to the inscribed ellipsoid. 6/Pi^2 is also the diameter of a circle whose circumference equals the ratio of surface area of a cube to the inscribed sphere. - Omar E. Pol, Oct 08 2011 6/(Pi^2 * n^2) is the probability that two randomly selected positive integers will have a greatest common divisor equal to n, n >= 1. - Geoffrey Critzer, May 28 2013 Equals lim_{n->infinity} (Sum_{k=1..n} phi(k)/k)/n, i.e., the limit mean value of phi(k)/k, where phi(k) is Euler's totient function. Proof is trivial using the formula for Sum_{k=1..n} phi(k)/k listed at the Wikipedia link. For the limit mean value of k/phi(k), see A082695. - Stanislav Sykora, Nov 14 2014 REFERENCES Hardy and Wright, 'An Introduction to the Theory of Numbers'. See Theorems 332 and 333. C. Pickover, Wonders of Numbers, Oxford University Press, NY, 2001, p. 359. LINKS Harry J. Smith, Table of n, a(n) for n = 0..20000 P. Diaconis and P. Erdos, On the distribution of the greatest common divisor, in A Festschrift for Herman Rubin, pp. 56-61, IMS Lecture Notes Monogr. Ser., 45, Inst. Math. Statist., Beachwood, OH, 2004 C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review H. J. Smith, XPCalc Eric Weisstein's World of Mathematics, Hafner-Sarnak-McCurley Constant Eric Weisstein's World of Mathematics, Relatively Prime Eric Weisstein's World of Mathematics, Squarefree Wikipedia, Euler's totient function FORMULA Equals 1/A013661. 6/Pi^2 = Product_{k>=1} (1 - 1/prime(k)^2) = Sum_{k>=1} mu(k)/k^2. - Vladeta Jovovic, May 18 2001 EXAMPLE .6079271018540266286632767792583658334261526480... MAPLE evalf(1/Zeta(2)) ; # R. J. Mathar, Mar 27 2013 MATHEMATICA RealDigits[ 6/Pi^2, 10, 105][] RealDigits[1/Zeta, 10, 111][] (* Robert G. Wilson v, Jan 20 2017 *) PROG (Harry J. Smith's VPcalc program): 150 M P x=6/Pi^2. (PARI) default(realprecision, 20080); x=60/Pi^2; for (n=0, 20000, d=floor(x); x=(x-d)*10; write("b059956.txt", n, " ", d)); \\ Harry J. Smith, Jun 30 2009 (MAGMA) R:= RealField(100); 6/(Pi(R))^2; // G. C. Greubel, Mar 09 2018 CROSSREFS See A002117 for further references and links. Cf. A005117 (squarefree numbers), A013661, A082695. Sequence in context: A249651 A021626 A320376 * A245700 A201521 A011393 Adjacent sequences:  A059953 A059954 A059955 * A059957 A059958 A059959 KEYWORD easy,nonn,cons AUTHOR Jason Earls, Mar 01 2001 STATUS approved

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Last modified October 18 00:21 EDT 2019. Contains 328135 sequences. (Running on oeis4.)