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 A101485 a(n) = (4n)! / ( 4^n * (2n)! ). 1
 1, 3, 105, 10395, 2027025, 654729075, 316234143225, 213458046676875, 191898783962510625, 221643095476699771875, 319830986772877770815625, 563862029680583509947946875, 1192568192774434123539907640625 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA sin(arcsin(2x)/2) = x + 3x^3/3! + 105x^5/5! + 10395x^7/7! +... E.g.f.: cosh(x^2/2). - Paul Barry, Sep 28 2010 a(n) = 4^n*Gamma(2*n+1/2) / Gamma(1/2). - Peter Luschny, Jul 05 2011 Hypergeom. recurrence: a(n) -(4*n-1)*(4*n-3)*a(n-1)=0. - R. J. Mathar, Sep 21 2012 MAPLE seq(4^n*pochhammer(1/2, 2*n), n=0..12); # Peter Luschny, Jul 05 2011 MATHEMATICA f[n_] := 4^n*Pochhammer[1/2, 2 n]; Array[f, 13, 0] (* Robert G. Wilson v, Jul 05 2011 *) PROG (PARI) a(n)=(4*n)!/(2*n)!>>(2*n) \\ Charles R Greathouse IV, Jul 06 2011 CROSSREFS Bisection of A001147. Odd part of A009120. Sequence in context: A215945 A075528 A271049 * A226236 A074072 A226074 Adjacent sequences:  A101482 A101483 A101484 * A101486 A101487 A101488 KEYWORD nonn,easy AUTHOR Ralf Stephan, Jan 21 2005 STATUS approved

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Last modified October 23 22:35 EDT 2019. Contains 328376 sequences. (Running on oeis4.)