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 A221209 Decimal expansion of two times the Catalan constant. 2
 1, 8, 3, 1, 9, 3, 1, 1, 8, 8, 3, 5, 4, 4, 3, 8, 0, 3, 0, 1, 0, 9, 2, 0, 7, 0, 2, 9, 8, 6, 4, 7, 6, 8, 2, 2, 1, 5, 4, 8, 2, 9, 8, 7, 4, 8, 5, 6, 3, 3, 4, 4, 2, 6, 8, 5, 3, 2, 9, 9, 6, 2, 3, 9, 2, 4, 3, 5, 2, 6, 0, 3, 9, 5, 5, 2, 5, 0, 9, 5, 3, 8, 9, 5, 8, 7, 1, 3, 0, 2, 5, 8, 5, 2, 2, 3, 0, 2, 1, 2 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES I.S. Gradshteyn and I.M. Ryzhik, Table of integrals, series and products, 5th edition, Academic Press, 1994, eq. (3.521.2). LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 FORMULA Equals Integral_{x=0..oo} x/cosh(x) dx. Equals 2*A006752. From Amiram Eldar, Aug 20 2020: (Start) Equals Integral_{x=0..Pi/2} x/sin(x) dx. Equals 1 + Integral_{x=0..oo} x * exp(-x) * tanh(x) dx. (End) EXAMPLE 1.83193118835443803010920702986476822154... MAPLE evalf(2*Catalan) ; MATHEMATICA RealDigits[2 Catalan, 10, 100][[1]] (* Bruno Berselli, Feb 21 2013 *) PROG (PARI) default(realprecision, 100); 2*Catalan \\ G. C. Greubel, Aug 25 2018 (MAGMA) SetDefaultRealField(RealField(100)); R:=RealField(); 2*Catalan(R); // G. C. Greubel, Aug 25 2018 CROSSREFS Cf. A006752. Sequence in context: A097890 A088453 A019782 * A056030 A195473 A195728 Adjacent sequences:  A221206 A221207 A221208 * A221210 A221211 A221212 KEYWORD nonn,cons,easy AUTHOR R. J. Mathar, Feb 21 2013 STATUS approved

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Last modified November 30 05:12 EST 2021. Contains 349419 sequences. (Running on oeis4.)