Double factorial

[salvomic]

(03-02-2015 04:18 PM)Han Wrote:  The wiki explains how you can calculate it using the regular factorial:
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It should be pretty easy to write your own program using these formulas. (Note: the wiki has a slight error ...

(03-02-2015 04:36 PM)Helge Gabert Wrote:  No error checking, but something along these lines

#cas
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Is this what you are asking (simple program)?

yes, thanks both!
so this should be enough "precise" and it is ok both in Home and CAS:

Code:


EXPORT factorial(n)
//Double factorial n!!
BEGIN
local f;
IF odd(n) THEN f:=product(X,X,,1,n,2);
ELSE f:=product(X,X,2,n,2); END;
RETURN(f);
END;

My memory failed, and I didn't remember "product()"

thanks again,
Salvo