Double factorial [wp34s]

[Gerson W. Barbosa]

(02-14-2016 03:24 PM)John Keith Wrote:  Hi Gerson,

I have never heard of this constant 13 SD! and can't find anything on Google either. Can you please enlighten me on this subject?

By the way, my HP50 gets 1.46163214497 in about 24.8s when running your program.

Hi John,

That is known as xmin, the value at which the Γ function is minimum for positive arguments. Just submit the result you've found to Wolfram Alpha and take a look at the first possible closed form. I ought to have provided the links previously, but I wanted to sparkle some curiosity.

By the way, the equation can be written more compactly as

x^2*(x^2 + x + 1)*(x^6 + x^3 + 1)*(x^18 + x^9 + 1) - 130615 = 0

Thanks for asking!

Gerson.

P.S.: By 13 SD I meant the approximation was good to 13 significant digits. Sorry for the confusion!

P.P.S.: I'd completely forgotten about an old thread started by Barry Mead. I think it should also be worth taking a look at:

http://www.hpmuseum.org/forum/thread-2508.html