HP 50g Double factorial

[joeres]

Hi Gilles,

(05-01-2019 01:40 PM)Gilles Wrote:  

Code:

 « -> n 'IFTE(n MOD 2,(n+1)!/(2^((n+1)/2)*((n+1)/2)!),2^(n/2)*(n/2)!)'»

returns 1 for zero, and an error for n<0
And works in symbolic mode with a symbolic variable

thanks for the answer with the short and sweet version.
I like that a question mark is displayed for negative numbers. However, at -1 and -2 not. This is certainly related to the formula?

Kind regards
Joerg