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#1 2012-10-28 20:51:18

Harold
Guest

Multifactorial

How do you define multifactorial?I know what it is,but how do you define it?I know how to define factorial.

#2 2012-10-28 21:12:14

anonimnystefy
Real Member
From: The Foundation
Registered: 2011-05-23
Posts: 15,507

Re: Multifactorial


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#3 2012-10-28 23:00:35

Harold
Guest

Re: Multifactorial

Can't this be another definition-

#4 2012-10-29 00:26:57

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,270

Re: Multifactorial

Hi Harold;

Did you try one? Say for k = 3.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#5 2012-10-29 00:48:16

Harold
Guest

Re: Multifactorial

Well,if I try n=11,k=3,then11!!!=11*8*5*2(as 11 mod 3=2) =880,is it correct?

#6 2012-10-29 01:09:14

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,270

Re: Multifactorial

Hi;

That is correct. Now what do you get for 20!!!! ?


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#7 2012-10-29 01:47:18

Harold
Guest

Re: Multifactorial

Well,thank you,I love solving problems,now,20!!!!,so n=20 and k=4
20!!!!=20(20-4)(20-4*2)(20-4*3)...(4) [as 20 mod 4=0]=20*16*12*8*4=122880.

#8 2012-10-29 01:57:27

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,270

Re: Multifactorial

Hi;

That is correct. Your formula looks fine to me. Although there is a better one on that page that anonimnystefy sent you.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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#9 2012-10-29 02:40:30

Harold
Guest

Re: Multifactorial

But,I am confused,if I do 11!!! by the method in wikipedia,I get 11!!!=11(8!!!)=11(8(5!!!))=11(8(5(2!!!)))=11(8(5(1))) [as 0<2<3] =440
and by my method,I get 11!!!=11(11-3)(11-2*3)...(2)=11*8*5*2=880
which is correct ??

#10 2012-10-29 02:44:34

bobbym
Administrator
From: Bumpkinland
Registered: 2009-04-12
Posts: 85,270

Re: Multifactorial

2!!! = 2 not 1.


In mathematics, you don't understand things. You just get used to them.
Of course that result can be rigorously obtained, but who cares?
Combinatorics is Algebra and Algebra is Combinatorics.

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