[seqfan] Re: definition of double factorial

Max Alekseyev maxale at gmail.com
Tue Oct 20 17:20:36 CEST 2009

OEIS says, for example:

%N A001147 Double factorial numbers: (2n-1)!! = 1.3.5....(2n-1).
%p A001147 A001147 := proc(n) doublefactorial(2*n-1); end: [From R. J.
Mathar (mathar(AT)strw.leidenuniv.nl), Jul 04 2009]

Maple's documentation for doublefactorial(n) reads in part:

"When n is a positive integer, this definition is equivalent to the product:
  * n(n-2)...(6)(4)(2) if n is an even, positive integer
  * n(n-2)...(5)(3)(1) if n is an odd, positive integer"

Where is the inconsistency?


On Tue, Oct 20, 2009 at 6:35 AM, Karol <penson at lptl.jussieu.fr> wrote:
> This is to inform you that the definition of double factorial numbers
>  as given in A001147(n) and  in related sequences as A001818(n)  etc.
> disagrees with Maple's
>    function doublefactorial(n). I do not know if this point was raised
> before.
>  As this may lead to inconsistencies  I intend to submit a comment on it.
>             Karol A.Penson
> _______________________________________________
> Seqfan Mailing list - http://list.seqfan.eu/

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