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A007685 a(n) = Product_{k=1..n} binomial(2*k,k).
(Formerly M2047)
11
1, 2, 12, 240, 16800, 4233600, 3911846400, 13425456844800, 172785629592576000, 8400837310791045120000, 1552105098192510332190720000, 1094904603628138948657963991040000, 2960792853328653706847125274154762240000, 30794022150329995743434211126374020153344000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

REFERENCES

H. W. Gould, A class of binomial sums and a series transform, Utilitas Math., 45 (1994), 71-83.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..50

H. W. Gould, A class of binomial sums and a series transform, Utilitas Math., 45 (1994), 71-83. (Annotated scanned copy)

FORMULA

a(0) = 1, a(n) = (2^(2*n)*a(n - 1)*Gamma(n + 1/2))/(sqrt(Pi)*Gamma(n + 1)). - Ilya Gutkovskiy, Sep 18 2015

a(n) = (2^(n^2 + n - 1/24)*A^(3/2)*Pi^(-n/2 - 1/4)*BarnesG(n + 3/2))/(e^(1/8)*BarnesG(n + 2)), where A is the Glaisher-Kinkelin constant (A074962), BarnesG is the Barnes G-function. - Ilya Gutkovskiy, Sep 18 2015

a(n) ~ A^(3/2) * 2^(n^2 + n - 7/24) * exp(n/2 - 1/8) / (Pi^((n+1)/2) * n^(n/2 + 3/8)), where A = A074962 is the Glaisher-Kinkelin constant. - Vaclav Kotesovec, Apr 16 2016

MAPLE

[seq(mul(binomial(2*k, k), k=1..n), n=0..16)];

MATHEMATICA

Table[Product[Binomial[2*k, k], {k, 1, n}], {n, 0, 50}] (* G. C. Greubel, Feb 02 2017 *)

PROG

(PARI) a(n) = prod(k=1, n, binomial(2*k, k)); \\ Michel Marcus, Sep 18 2015

CROSSREFS

Cf. A000984, A001142, A112332, A268196.

Sequence in context: A141083 A257665 A132877 * A132987 A087046 A111403

Adjacent sequences:  A007682 A007683 A007684 * A007686 A007687 A007688

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified June 12 15:58 EDT 2021. Contains 344957 sequences. (Running on oeis4.)