what is factorial language?

[zeeshanmcs]

what is factorial language?

[sanam]

Please don't get confused as language given here is as sequence of characters (1...9) , so any word in this language will be finite string made of 0...9 letters, like 4!= 24 and so on...
When you will see recursive definition of factorial then you will find the expression you want i.e n(n-1)...0!
Note that any number however huge it is, is always made up of 0 to 9 letters in any combination.