what is fictorial ?

The term is "factorial".....it represents the product of the first "n" positive integers and is written as n!

Thus,

3! = The product of the first three positive integers = 3*2*1 = 6

And 5! = The product of the first five positive integers = 5*4*3*2*1 = 120

This idea is used quite frequently in the areas of probability and statistics to count sets or orderings of things.

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Proof that...... (0! = 1).......while not a "formal" proof, here's the idea........

3! = 3*2*1
2! = 2*1 = (3*2*1)/3 = 3!/3
1! = (2*1)/2 = 2!/2
Then.....
0! = 1!/1 = 1

   

Thanks Chris. 

A neat little demonstration.