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 A268813 Decimal expansion of sum(k>=0, 1/C(k)), where C(k) is a Catalan Number (A000108). 4
 2, 8, 0, 6, 1, 3, 3, 0, 5, 0, 7, 7, 0, 7, 6, 3, 4, 8, 9, 1, 5, 2, 9, 2, 3, 6, 7, 0, 0, 6, 3, 1, 8, 0, 3, 2, 5, 4, 5, 9, 5, 8, 4, 9, 9, 9, 1, 5, 2, 3, 2, 9, 1, 4, 4, 6, 9, 7, 7, 2, 6, 6, 3, 7, 9, 5, 0, 2, 7, 6, 9, 6, 9, 3, 8, 9, 4, 9, 0, 6, 1, 4, 9, 7, 0, 7, 2, 2, 2, 1, 6, 9, 8, 3, 1, 3, 7, 8, 5, 2, 8, 2 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 Eric Weisstein's MathWorld, Catalan Number. Wikipedia, Catalan number FORMULA Equals 2 + 4*Pi/(9*sqrt(3)) = 1 + A121839. Also equals 2F1(1, 2; 1/2; 1/4), where 2F1 is the hypergeometric function 2F1. EXAMPLE 2.80613305077076348915292367006318032545958499915232914469772663795... MATHEMATICA RealDigits[2 + 4*Pi/(9*Sqrt[3]), 10, 102][[1]] PROG (PARI) default(realprecision, 100); 2 + 4*Pi/(9*sqrt(3)) \\ G. C. Greubel, Nov 04 2018 (MAGMA) SetDefaultRealField(RealField(100)); R:=RealField(); 2 + 4*Pi(R)/(9*Sqrt(3)); // G. C. Greubel, Nov 04 2018 CROSSREFS Cf. A000108, A121839 (which is the main entry for this constant). Sequence in context: A321595 A188924 A011055 * A242056 A195009 A020860 Adjacent sequences:  A268810 A268811 A268812 * A268814 A268815 A268816 KEYWORD nonn,cons AUTHOR Jean-François Alcover, Feb 14 2016 STATUS approved

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Last modified January 19 20:01 EST 2019. Contains 319309 sequences. (Running on oeis4.)