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 A013661 Decimal expansion of Pi^2/6 = zeta(2) = Sum_{m>=1} 1/m^2. 331
 1, 6, 4, 4, 9, 3, 4, 0, 6, 6, 8, 4, 8, 2, 2, 6, 4, 3, 6, 4, 7, 2, 4, 1, 5, 1, 6, 6, 6, 4, 6, 0, 2, 5, 1, 8, 9, 2, 1, 8, 9, 4, 9, 9, 0, 1, 2, 0, 6, 7, 9, 8, 4, 3, 7, 7, 3, 5, 5, 5, 8, 2, 2, 9, 3, 7, 0, 0, 0, 7, 4, 7, 0, 4, 0, 3, 2, 0, 0, 8, 7, 3, 8, 3, 3, 6, 2, 8, 9, 0, 0, 6, 1, 9, 7, 5, 8, 7, 0 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS "In 1736 he [Leonard Euler, 1707-1783] discovered the limit to the infinite series, Sum 1/n^2. He did it by doing some rather ingenious mathematics using trigonometric functions that proved the series summed to exactly Pi^2/6. How can this be? ... This demonstrates one of the most startling characteristics of mathematics - the interconnectedness of, seemingly, unrelated ideas." - Clawson [See Hardy and Wright, Theorems 332 and 333. - N. J. A. Sloane, Jan 20 2017] Also dilogarithm(1). - Rick L. Shepherd, Jul 21 2004 Also Integral_{x>=0} x/(exp(x)-1) dx. [Abramowitz-Stegun, 23.2.7., for s=2, p. 807] For the partial sums see the fractional sequence A007406/A007407. Pi^2/6 is also the length of the circumference of a circle whose diameter equals the ratio of volume of an ellipsoid to the circumscribed cuboid. Pi^2/6 is also the length of the circumference of a circle whose diameter equals the ratio of surface area of a sphere to the circumscribed cube. - Omar E. Pol, Oct 07 2011 1 < n^2/(eulerphi(n)*sigma(n)) < zeta(2) for n > 1. - Arkadiusz Wesolowski, Sep 04 2012 Volume of a sphere inscribed in a cube of volume Pi. More generally, Pi^x/6 is the volume of an ellipsoid inscribed in a cuboid of volume Pi^(x-1). - Omar E. Pol, Feb 17 2016 Surface area of a sphere inscribed in a cube of surface area Pi. More generally, Pi^x/6 is the surface area of a sphere inscribed in a cube of surface area Pi^(x-1). - Omar E. Pol, Feb 19 2016 zeta(2)+1 is a weighted average of the integers, n > 2, using zeta(n)-1 as the weights for each n. We have: Sum_{n >= 2} (zeta(n)-1) = 1 and Sum_{n >= 2} n*(zeta(n)-1) = zeta(2)+1. - Richard R. Forberg, Jul 14 2016 zeta(2) is the expected value of sigma(n)/n. - Charlie Neder, Oct 22 2018 Graham shows that a rational number x can be expressed as a finite sum of reciprocals of distinct squares if and only if x is in [0, Pi^2/6-1) U [1, Pi^2/6). See section 4 for other results and Theorem 5 for the underlying principle. - Charles R Greathouse IV, Aug 04 2020 REFERENCES M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 811. F. Aubonnet, D. Guinin and B. Joppin, Précis de Mathématiques, Analyse 2, Classes Préparatoires, Premier Cycle Universitaire, Bréal, 1990, Exercice 908, pages 82 and 91-92. Calvin C. Clawson, Mathematical Mysteries, The Beauty and Magic of Numbers, Perseus Books, 1996, p. 97. W. Dunham, Euler: The Master of Us All, The Mathematical Association of America, Washington, D.C., 1999, p. xxii. Hardy and Wright, 'An Introduction to the Theory of Numbers'. See Theorems 332 and 333. A. A. Markoff, Mémoire sur la transformation de séries peu convergentes en séries très convergentes, Mém. de l'Acad. Imp. Sci. de St. Pétersbourg, XXXVII, 1890. G. F. Simmons, Calculus Gems, Section B.15, B.24, pp. 270-271, 323-325, McGraw Hill, 1992. Arnold Walfisz, Weylsche Exponentialsummen in der neueren Zahlentheorie, Deutscher Verlag der Wissenschaften, Berlin, 1963, p. 99, Satz 1. A. Weil, Number theory: an approach through history; from Hammurapi to Legendre, Birkhäuser, Boston, 1984; see p. 261. David Wells, The Penguin Dictionary of Curious and Interesting Numbers, Revised Edition, Penguin Books, London, England, 1997, page 23. LINKS Harry J. Smith, Table of n, a(n) for n = 1..20000 M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy]. D. H. Bailey, J. M. Borwein and D. M. Bradley, Experimental determination of Apéry-like identities for zeta(4n+2), arXiv:math/0505270 [math.NT], 2005-2006. Peter Bala, New series for old functions Peter Bala, Formulas for A013661 David Benko and John Molokach, The Basel Problem as a Rearrangement of Series, The College Mathematics Journal, Vol. 44, No. 3 (May 2013), pp. 171-176. R. Calinger, Leonard Euler: The First St. Petersburg Years (1727-1741), Historia Mathematica, Vol. 23, 1996, pp. 121-166. R. Chapman, Evaluating Zeta(2):14 Proofs to Zeta(2)= (pi)^2/6 R. W. Clickery, Probability of two numbers being coprime Alessio Del Vigna, On a solution to the Basel problem based on the fundamental theorem of calculus, arXiv:2104.01710 [math.HO], 2021. Leonhard Euler, On the sums of series of reciprocals, arXiv:math/0506415 [math.HO], 2005-2008. Leonhard Euler, De summis serierum reciprocarum, E41. R. L. Graham, On finite sums of unit fractions, Proceedings of the London Mathematical Society, s3-14 (1964), pp. 193-207. doi:10.1112/plms/s3-14.2.193 Michael D. Hirschhorn, A simple proof that zeta(2) = Pi^2/6, The Mathematical Intelligencer 33:3 (2011), pp 81-82. Melissa Larson, Verifying and discovering BBP-type formulas, 2008. Alain Lasjaunias and Jean-Paul Tran, A note on the equality Pi^2/6 = Sum_{n>=1} 1/n^2, arXiv:2312.02245 [math.HO], 2023. Math. Reference Project, The Zeta Function, Zeta(2) Math. Reference Project, The Zeta Function, Odds That Two Numbers Are Coprime" R. Mestrovic, Euclid's theorem on the infinitude of primes: a historical survey of its proofs (300 BC--2012) and another new proof, arXiv preprint arXiv:1202.3670 [math.HO], 2012. Jon Perry, Prime Product Paradox Simon Plouffe, Plouffe's Inverter, Zeta(2) or Pi**2/6 to 100000 digits Simon Plouffe, Zeta(2) or Pi**2/6 to 10000 places Simon Plouffe, Zeta(2) to Zeta(4096) to 2048 digits each (gzipped file) A. L. Robledo, value of the Riemann zeta function at s=2, PlanetMath.org. E. Sandifer, How Euler Did It, Estimating the Basel Problem E. Sandifer, How Euler Did It, Basel Problem with Integrals C. Tooth, Pi squared over six Eric Weisstein's World of Mathematics, Dilogarithm. Eric Weisstein's World of Mathematics, Riemann Zeta Function zeta(2). Wikipedia, Basel Problem Wikipedia, Bailey-Borwein-Plouffe formula. Herbert S. Wilf, Accelerated series for universal constants, by the WZ method, Discrete Mathematics & Theoretical Computer Science, Vol 3, No 4 (1999). Index entries for transcendental numbers Index entries for zeta function. FORMULA Limit_{n->oo} (1/n)*(Sum_{k=1..n} frac((n/k)^(1/2))) = zeta(2) and in general we have lim_{n->oo} (1/n)*(Sum_{k=1..n} frac((n/k)^(1/m))) = zeta(m), m >= 2. - Yalcin Aktar, Jul 14 2005 Equals Integral_{x=0..1} (log(x)/(x-1)) dx or Integral_{x>=1} (log(x/(x-1))/x) dx. - Jean-François Alcover, May 30 2013 For s >= 2 (including Complex), zeta(s) = Product_{n >= 1} prime(n)^s/(prime(n)^s - 1). - Fred Daniel Kline, Apr 10 2014 Also equals 1 + Sum_{n>=0} (-1)^n*StieltjesGamma(n)/n!. - Jean-François Alcover, May 07 2014 zeta(2) = Sum_{n>=1} ((floor(sqrt(n)) - floor(sqrt(n-1)))/n). - Mikael Aaltonen, Jan 10 2015 zeta(2) = Sum_{n>=1} (((sqrt(5)-1)/2/sqrt(5))^n/n^2) + Sum_{n>=1} (((sqrt(5)+1)/2/sqrt(5))^n/ n^2) + log((sqrt(5)-1)/2/sqrt(5))log((sqrt(5)+1)/2/sqrt(5)). - Seiichi Kirikami, Oct 14 2015 The above formula can also be written zeta(2) = dilog(x) + dilog(y) + log(x)*log(y) where x = (1-1/sqrt(5))/2 and y=(1+1/sqrt(5))/2. - Peter Luschny, Oct 16 2015 zeta(2) = Integral_{x>=0} 1/(1 + e^x^(1/2)) dx, because (1 - 1/2^(s-1))*Gamma[1 + s]*Zeta[s] = Integral_{x>=0} 1/(1 + e^x^(1/s)) dx. After Jean-François Alcover in A002162. - Mats Granvik, Sep 12 2016 zeta(2) = Product_{n >= 1} (144*n^4)/(144*n^4 - 40*n^2 + 1). - Fred Daniel Kline, Oct 29 2016 zeta(2) = lim_{n->oo} (1/n) * Sum_{k=1..n} A017665(k)/A017666(k). - Dimitri Papadopoulos, May 10 2019 [See the Walfisz reference, and a comment in A284648, citing also the Sándor et al. Handbook. - Wolfdieter Lang, Aug 22 2019] Equals Sum_{k>=1} H(k)/(k*(k+1)), where H(k) = A001008(k)/A002805(k) is the k-th harmonic number. - Amiram Eldar, Aug 16 2020 Equals (8/3)*(1/2)!^4 = (8/3)*Gamma(3/2)^4. - Gary W. Adamson, Aug 17 2021 Equals ((m+1)/m) * Integral_{x=0..1} log(Sum _{k=0..m} x^k )/x dx, m > 0 (Aubonnet reference). - Bernard Schott, Feb 11 2022 Equals 1 + Sum_{n>=2} Sum_{i>=n+1} (zeta(i)-1). - Richard R. Forberg, Jun 04 2023 EXAMPLE 1.6449340668482264364724151666460251892189499012067984377355582293700074704032... MAPLE evalf(Pi^2/6, 120); # Muniru A Asiru, Oct 25 2018 # Calculates an approximation with n exact decimal places (small deviation # in the last digits are possible). Goes back to ideas of A. A. Markoff 1890. zeta2 := proc(n) local q, s, w, v, k; q := 0; s := 0; w := 1; v := 4; for k from 2 by 2 to 7*n/2 do w := w*v/k; q := q + v; v := v + 8; s := s + 1/(w*q); od; 12*s; evalf[n](%) end: zeta2(1000); # Peter Luschny, Jun 10 2020 MATHEMATICA RealDigits[N[Pi^2/6, 100]][[1]] RealDigits[Zeta[2], 10, 120][[1]] (* Harvey P. Dale, Jan 08 2021 *) PROG (PARI) default(realprecision, 200); Pi^2/6 (PARI) default(realprecision, 200); dilog(1) (PARI) default(realprecision, 200); zeta(2) (PARI) A013661(n)={localprec(n+2); Pi^2/.6\10^n%10} \\ Corrected and improved by M. F. Hasler, Apr 20 2021 (PARI) default(realprecision, 20080); x=Pi^2/6; for (n=1, 20000, d=floor(x); x=(x-d)*10; write("b013661.txt", n, " ", d)); \\ Harry J. Smith, Apr 29 2009 (PARI) sumnumrat(1/x^2, 1) \\ Charles R Greathouse IV, Jan 20 2022 (Maxima) fpprec : 100\$ ev(bfloat(zeta(2)))\$ bfloat(%); /* Martin Ettl, Oct 21 2012 */ (Magma) pi:=Pi(RealField(110)); Reverse(Intseq(Floor(10^105*pi^2/6))); // Vincenzo Librandi, Oct 13 2015 (Python) # Use some guard digits when computing. # BBP formula (3 / 16) P(2, 64, 6, (16, -24, -8, -6, 1, 0)). from decimal import Decimal as dec, getcontext def BBPzeta2(n: int) -> dec: getcontext().prec = n s = dec(0); f = dec(1); g = dec(64) for k in range(int(n * 0.5536546824812272) + 1): sixk = dec(6 * k) s += f * ( dec(16) / (sixk + 1) ** 2 - dec(24) / (sixk + 2) ** 2 - dec(8) / (sixk + 3) ** 2 - dec(6) / (sixk + 4) ** 2 + dec(1) / (sixk + 5) ** 2 ) f /= g return (s * dec(3)) / dec(16) print(BBPzeta2(2000)) # Peter Luschny, Nov 01 2023 CROSSREFS Cf. A001008 (H(n): numerators), A002805 (denominators), A013679 (continued fraction), A002117 (zeta(3)), A013631 (cont.frac. for zeta(3)), A013680 (cont.frac. for zeta(4)), 1/A059956, A108625, A142995, A142999. Sequence in context: A201587 A110756 A200698 * A209273 A330934 A019174 Adjacent sequences: A013658 A013659 A013660 * A013662 A013663 A013664 KEYWORD cons,nonn,nice AUTHOR N. J. A. Sloane EXTENSIONS Edited by N. J. A. Sloane, Nov 22 2023 STATUS approved

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Last modified February 27 08:19 EST 2024. Contains 370367 sequences. (Running on oeis4.)