Re: PARI/GP wrong on 7!!+7+1 being not prime, or oeis.org/Mathematica?

[hermann@stamm-wilbrandt.de]

On 2025-08-28 14:16, Vincent Delecroix wrote:
> The n!! notation is rather standard in combinatorics, see eg
>
> https://en.wikipedia.org/wiki/Double_factorial
> Best
> Vincent
Thanks, that explains it.

!! is not mentioned in "2.4 GP operators":
https://pari.math.u-bordeaux.fr/pub/pari/manuals/2.17.2/users.pdf#page=29

It is implemented in Mathematica:
https://reference.wolfram.com/language/ref/Factorial2.html


@Bill, you once added primorial operator after first stating "not 
needed".

$ gp -q
? version
[2, 16, 1]
? 7#
210
?

Are you in the mood of adding another operator (!!) to GP?

Regards,

Hermann.