HP 50g Double factorial

[John Keith]

(05-01-2019 04:14 PM)Gilles Wrote:  A negative or not integer input will result an error "Bad argument value".

Not necessarily. See this thread.

Here is a version for the HP-48 or HP 50:

Code:


\<< \pi EVAL DUP2 * COS 1. - .25 * SWAP .5 * SWAP ^ SWAP .5 * DUP 2. SWAP ^ SWAP 1. + GAMMA * *
\>>

It will handle non-integer arguments, and complex numbers if complex mode is enabled. Negative even integers return results near negative infinity.

See the graphs here.