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 A085565 Decimal expansion of lemniscate constant A. 13
 1, 3, 1, 1, 0, 2, 8, 7, 7, 7, 1, 4, 6, 0, 5, 9, 9, 0, 5, 2, 3, 2, 4, 1, 9, 7, 9, 4, 9, 4, 5, 5, 5, 9, 7, 0, 6, 8, 4, 1, 3, 7, 7, 4, 7, 5, 7, 1, 5, 8, 1, 1, 5, 8, 1, 4, 0, 8, 4, 1, 0, 8, 5, 1, 9, 0, 0, 3, 9, 5, 2, 9, 3, 5, 3, 5, 2, 0, 7, 1, 2, 5, 1, 1, 5, 1, 4, 7, 7, 6, 6, 4, 8, 0, 7, 1, 4, 5, 4 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS This number is transcendental by a result of Schneider on elliptic integrals. - Benoit Cloitre, Jan 08 2006 The two lemniscate constants are A = Integral_{x = 0..1} 1/sqrt(1 - x^4) dx and B = Integral_{x = 0..1} x^2/sqrt(1 - x^4) dx. See A076390. - Peter Bala, Oct 25 2019 REFERENCES Th. Schneider, Transzendenzuntersuchungen periodischer Funktionen (1934). Th. Schneider, Arithmetische Untersuchungen elliptischer Integrale (1937). LINKS G. C. Greubel, Table of n, a(n) for n = 1..5000 S. Khrushchev, Orthogonal polynomials and continued fractions from Euler’s point of view, Encyclopedia of Mathematics and its Applications 122. J. Todd, The lemniscate constants, Comm. ACM, 18 (1975), 14-19; 18 (1975), 462. J. Todd, The lemniscate constants, in Pi: A Source Book, pp. 412-417. Eric Weisstein's World of Mathematics, Lemniscate Constant FORMULA Equals (1/4)*(2*Pi)^(-1/2)*GAMMA(1/4)^2. Equals Integral_{x>=1}dx/sqrt(4x^3-4x). - Benoit Cloitre, Jan 08 2006 Equals Product_(k>=0, [(4k+3)(4k+2)] / [(4k+5)(4k+4)] ) (Gauss). - Ralf Stephan, Mar 04 2008 Equals Pi/sqrt(8)/agm(1,sqrt(1/2)). Equals Pi/sqrt(8)*hypergeom([1/2,1/2],,1/2). Prod_{m>=1} ((2*m)/(2*m+1))^(-1)^m. - Jean-François Alcover, Sep 02 2014, after Steven Finch. From Peter Bala, Mar 09 2015: (Start) Equals Integral_{x = 0..1} 1/sqrt(1 - x^4) dx. Continued fraction representations: 2/(1 + 1*3/(2 + 5*7/(2 + 9*11/(2 + ... )))) due to Euler - see Khrushchev, p. 179. Also equals 1 + 1/(2 + 2*3/(2 + 4*5/(2 + 6*7/(2 + ... )))). (End) From Peter Bala, Oct 25 2019: (Start) Equals 1 + 1/5 + (1*3)/(5*9) + (1*3*5)/(5*9*13) + ... = hypergeom([1/2,1],[5/4],1/2) by Gauss's second summation theorem. Equivalently, define a sequence of rational numbers r(n) recursively by r(n) = (2*n - 3)/(4*n - 3)*r(n-1) with r(1) = 1. Then the constant equals Sum_{n >= 1} r(n) = 1 + 1/5 + 1/15 + 1/39 + 7/663 + 1/221 + 11/5525 + 11/12325 + 1/2465 + .... The partial sum of the series to 100 terms gives 32 correct decimal digits for the constant. Equals (1*3)/(1*5) + (1*3*5)/(1*5*9) + (1*3*5*7)/(1*5*9*13) + ... = (3/5) * hypergeom([5/2,1],[9/4],1/2). (End) Equals (3/2)*A225119. - Peter Bala, Oct 27 2019 EXAMPLE 1.3110287771460599052324197949455597068413774757158115814084108519... MATHEMATICA RealDigits[ Gamma[1/4]^2/(4*Sqrt[2*Pi]), 10, 99][] (* or *) RealDigits[ EllipticK[-1], 10, 99][] (* Jean-François Alcover, Mar 07 2013, updated Jul 30 2016 *) PROG (PARI) gamma(1/4)^2/4/sqrt(2*Pi) (PARI) K(x)=Pi/2/agm(1, sqrt(1-x)) K(-1) \\ Charles R Greathouse IV, Aug 02 2018 (MAGMA) C := ComplexField(); [Gamma(1/4)^2/(4*Sqrt(2*Pi(C)))]; // G. C. Greubel, Nov 05 2017 CROSSREFS Cf. A076390, A225119. Sequence in context: A011354 A143119 A220419 * A216677 A196057 A058395 Adjacent sequences:  A085562 A085563 A085564 * A085566 A085567 A085568 KEYWORD nonn,cons AUTHOR N. J. A. Sloane, Jul 06 2003 STATUS approved

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Last modified November 12 04:21 EST 2019. Contains 329051 sequences. (Running on oeis4.)