2
$\begingroup$

This question already has an answer here:

Quick google search for factorial of non-integers led me to gamma function. I tried that in my calculator and it worked as expected for non-integers. Perhaps implements gamma function internally.

Now, for all positive numbers:

x < y => x! < y! 

But not for numbers between 0 and 1. 0! = 1!. I played around to find this:

0!      1
0.1!    0.951
0.4!    0.887
0.425!  0.886
0.45!   0.885
0.5!    0.886
0.55!   0.888
0.6!    0.893
0.9!    0.96
1!      1

What is the floor for the gamma function (or the unrestricted by integers factorial function)? The floor is around 0.45 from the table. I'm curious to know what is the floor value and the number for which gamma is minimum.

Any significance or implications of these numbers would be interesting too.

$\endgroup$

marked as duplicate by Lucian, user7530, user98602, apnorton, Joel Reyes Noche Dec 17 '14 at 4:32

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 2
    $\begingroup$ Compare math.stackexchange.com/questions/3245/… $\endgroup$ – Martin R Dec 10 '14 at 18:50
  • $\begingroup$ That's baffling! Why would 1.5! be less than 1? Besides, calculator says otherwise. $\endgroup$ – kBisla Dec 10 '14 at 18:56
  • 1
    $\begingroup$ $\Gamma(n) = (n-1)!$ for positive integers ... $\endgroup$ – Martin R Dec 10 '14 at 19:01
  • $\begingroup$ Got it, thanks! $\endgroup$ – kBisla Dec 10 '14 at 19:03
2
$\begingroup$

As Martin R says, there is no known simple closed form for the minimum of the Gamma function. However, for fun, here are the first 1000 digits of the root (in Mathematica):

FindRoot[D[Gamma[x], x], {x, 1.5}, WorkingPrecision -> 1000]

which produces

1.46163214496836234126265954232572132846819620400644635129598840859878\
6440353801810243074992733725592750556793365533053341617365778466985829\
1771683816450246525426187920443843819783335597739619760747194319349371\
7541405945193010996372416652777217279167325088046396007693297814490147\
5185803414306536810631010706016949785457933765577116113646852653864407\
7372589890682262958196750529119944311972207258664056482074952272808066\
6492780264672546913947612363653574355170333094944302512419288581347767\
7638037268207228647702315131118425758160327915893181546219377794692453\
7619116776460200864228324583987363497206740454783034481431732283690209\
3646770017559017693843888399883958228679946842407928700859042045977138\
8194093679122118848402487784207298777528715900614407383331513574002791\
5353912845037515421736664287138645800903908013264994637024811461027624\
7799875927238664920666176370867887038347260422463147415264091765916362\
0499923428977096412741183720620861677533192913168549317959136215151559\
088748352371795155035
$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.