Function FACTRL(N)
    Dim A(33)
    NTOP = 0
    A(1) = 1#
    If N < 0 Then
        Print "negative factorial"
        Exit Function
    ElseIf N <= NTOP Then
        FACTRL = A(N + 1)
    ElseIf N <= 32 Then
        For J = NTOP + 1 To N
            A(J + 1) = J * A(J)
        Next J
        NTOP = N
        FACTRL = A(N + 1)
    Else
        FACTRL = Exp(GAMMLN(N + 1#))
    End If
End Function