Factorial is a special result for a non-negative number. It can be represented by symbol '!'.
It is defined as: n! = n*(n-1)! (uptil 1)
Going by definition, we have
1!=1
2!=2
3!=6
4!=24
5!=12r
and so on..
Also, it is important to note that 0!=1, since 1 = 1! = 1*0!
Logic[]
Here is the prolog code for factorial of a number:
factorial(0,1). factorial(A,B):-A>0,A1=A-1,factorial(A1,B1),B=A*B1.