2n！ ! = 2n×(2n-2)×(2n-4)×n ....

2n！ = 2n×(2n- 1)×(2n-2)× 1 ..

Factorial factor is an operation symbol invented by Keyston Kramp (1760 ~1826) in 1808, and it is a mathematical term.

The factorial of a positive integer is the product of all positive integers less than or equal to this number, and the factorial of 0 is 1. The factorial writing of natural number n! . In 1808, Keyston Kaman introduced this symbol.

Because the factorial of a positive integer is a continuous multiplication operation, the result of multiplying 0 by any real number is 0. Therefore, we can't generalize or deduce 0 with the definition of positive integer factorial! = 1. That is, "0! = 1"。

Give "0!" The definition is only to facilitate the expression and operation of related formulas.

In discrete mathematics? In the definition of combination number, for positive integers,

It is just a factorial symbol on the special "form" defined. It can't be demonstrated by deduction.

"? Why 0! = 1 "What's the problem? False question, and beginners always ask this false question. Does this mean that we didn't put it in textbooks and teaching practice? "About 0! = 1' is just a concept of' definition'.

Of course, it is a big mistake to regard the above necessity and rationality as the derivation process of some teaching AIDS. Necessity and rationality are just a few limited examples, "0! The definition of = 1 "cannot be proved by a few examples.