Fortran functions returning unexpected types and values

I'm working on a project that needs to implement few numerical methods in Fortran. For this, I need to write some recursive functions. Here is my code.

!     
! File:   main.F95
!

RECURSIVE FUNCTION integrate(n) RESULT(rv)
    IMPLICIT NONE
    DOUBLE PRECISION :: rv
    INTEGER, INTENT(IN) :: n
    DOUBLE PRECISION, PARAMETER :: minusone = -1.0
    IF (n == 1) THEN
        rv = 10 !exp(minusone)
        RETURN
    ELSE
        rv = 1 - (n * integrate(n - 1))
        RETURN
    END IF
END FUNCTION integrate

RECURSIVE FUNCTION factorial(n) RESULT(res)
    INTEGER res, n
    IF (n .EQ. 0) THEN
        res = 1
    ELSE
        res = n * factorial(n - 1)
    END IF
END

PROGRAM main
    DOUBLE PRECISION :: rv1
    PRINT *, factorial(5)
    PRINT *, integrate(2)

    !READ *, rv1

END PROGRAM main

For this program the output is:

         NaN
       1

If I change the order of the print statements (line 30 & 31), the output will be:

         1
-19.000000

Output should be (for the original print statement order):

  120  
  -19 

I took the factorial function from the Wikipedia Fortran 95 language features page.

• Compiler : gfortran 4.5.3 with Cygwin
• IDE: Netbeans 7.0.1
• Platform: Windows 7