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 A122216 Numerators in infinite products for Pi/2, e and e^gamma (unreduced). 6
 1, 2, 4, 32, 4096, 201326592, 3283124128353091584, 26520146032764463901929624736590416838656, 840987221884558487834659180201583257033385988411167452990072842049923846092011283152896 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Mohammad K. Azarian, Euler's Number Via Difference Equations, International Journal of Contemporary Mathematical Sciences, Vol. 7, 2012, No. 22, pp. 1095 - 1102. J. Guillera and J. Sondow, Double integrals and infinite products for some classical constants via analytic continuations of Lerch's transcendent, arXiv:math/0506319 [math.NT], 2005-2006; Ramanujan J. 16 (2008) 247-270. J. Sondow, A faster product for Pi and a new integral for ln Pi/2, arXiv:math/0401406 [math.NT], 2004. J. Sondow, A faster product for Pi and a new integral for ln(Pi/2), Amer. Math. Monthly 112 (2005), 729-734 and 113 (2006), 670. FORMULA a(n) = Product_{k=1..ceiling(n/2)} (2k)^binomial(n,2k-1). EXAMPLE Pi/2 = (2/1)^(1/2) * (4/3)^(1/4) * (32/27)^(1/8) * (4096/3645)^(1/16) * ..., e = (2/1)^(1/1) * (4/3)^(1/2) * (32/27)^(1/3) * (4096/3645)^(1/4) * ... and e^gamma = (2/1)^(1/2) * (4/3)^(1/3) * (32/27)^(1/4) * (4096/3645)^(1/5) * .... MATHEMATICA a[n_] := Product[(2k)^Binomial[n, 2k-1], {k, 1, n/2 // Ceiling}]; Table[a[n], {n, 0, 8}] (* Jean-François Alcover, Nov 18 2018 *) CROSSREFS Cf. A092798. Denominators are A122217. Reduced numerators are A122214. Sequence in context: A062740 A336832 A122214 * A100117 A073888 A114642 Adjacent sequences: A122213 A122214 A122215 * A122217 A122218 A122219 KEYWORD frac,nonn AUTHOR Jonathan Sondow, Aug 26 2006 EXTENSIONS Offset and truncated term 840987221884... corrected by Jean-François Alcover, Nov 18 2018 STATUS approved

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