INTEGER FACTORIAL

      DO N=1,12
        WRITE (6,*) N,' factorial is ',FACTORIAL(N)
      END DO
      END

      OPTIONS /RECURSIVE
      INTEGER FUNCTION FACTORIAL (N)
!
! The Factorial of an integer N is N * N-1 * N-2 ... * 1.  
! This is often written as N!.
!
! If N is greater than 1, call ourselves recursively, 
! passing N-1 to perform the calculation.  Note that 
! each recursive call to FACTORIAL will get its own 
! copy of N.
!
! If N is 1 or less, the result is 1.  (We assume that
! N is not negative.)
!
      IF (N .GT. 1) THEN
        FACTORIAL = FACTORIAL(N-1) * N
      ELSE
        FACTORIAL = 1
      END IF

      RETURN
      END