Number Magic 


Question : 
What is a 'SubFactorial' ? 
Answer : 
To find the subfactorial of an integer, supposing 'n' is the integer the subfactorial of
n = n! x ((1/2)!  (1/3)! + (1/4)! . . . ((1)n) / n!)

For example the subfactorial of 4 :
= 4! ((1/2)!  (1/3)! + (1/4)!)
= 24 ((1/2)  (1/6) + (1/24))
= 9

