Why does zero factorial (0!) equal one, i.e. 0! = 1?

You can download all the important posts as  PDF book "Unlocking the Secrets of Quantitative Thinking".

Here are the most useful links with answers why does zero factorial equal one, i.e. 0! = 1:

http://www.quora.com/Mathematics/Why-does-zero-factorial-0-equal-one

http://wiki.answers.com/Q/Why_is_zero_factorial_equal_to_one

http://en.wikipedia.org/wiki/Factorial

http://math.stackexchange.com/questions/25333/why-does-0-1

https://ca.answers.yahoo.com/question/index?qid=20090116132324AACQIGU

http://www.zero-factorial.com/whatis.html

 http://statistics.about.com/od/ProbHelpandTutorials/a/Why-Does-Zero-Factorial-Equal-One.htm

http://mathforum.org/library/drmath/view/57128.html



[factorial, factoriel, factorial function, zero factorial]

What is Mathematics?

You can download all the important posts as  PDF book "Unlocking the Secrets of Quantitative Thinking".

Here is the link for the essay " A Mathematician's Lament" by Paul Lockhart.

"What is Mathematics, Really?" by Reuben Hersh, in Google Books.

"What is Mathematics? An Elementary Approach to Ideas and Methods", Richard Courant, Herbert Robbins, in Google Books.

Mathematical Intuition (Poincaré, Polya, Dewey) by Reuben Hersh, University of New Mexico, TMME, vol8, nos.1&2, p .35

 The Number Sense : How the Mind Creates Mathematics, by Stanislas Dehaene, Google Books.

The Psychology of Number and its Applications to Methods of Teaching Arithmetic by James A. McLellan; John Dewey, at www.openlibrary.org.

How Math Can Be Applied To So Many Different Fields, Mathematics and Quantitative Reasoning web site, B. Harford