# Why is the zero factorial one i.e ($0!=1$)? [duplicate]

Possible Duplicate:
Prove $0! = 1$ from first principles
Why does 0! = 1?

I was wondering why,

$0! = 1$

Thanks.

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## marked as duplicate by Srivatsan, mixedmath♦, Rahul, Brian M. Scott, yunoneSep 26 '11 at 19:21

You might be interested in this: en.wikipedia.org/wiki/Empty_product. –  Srivatsan Sep 26 '11 at 19:12
Possible duplicate of 25333, 25794 and 20969. –  Srivatsan Sep 26 '11 at 19:14
I've posted a new answer to the "possible duplicate" question, and I think it's simpler than all others. –  Michael Hardy Sep 26 '11 at 20:21
Can the downvoter explain him/herself? –  Srivatsan Sep 26 '11 at 22:17

Answer 2: $(n-1)! = \frac {n!} n$ applied with $n=1$