def fva(a, i, n):
    """ This function is for the future value of money
    over a period of time.
    a = Periodic Investment (1000)
    i = interest rate as decimal (.0675)
    n = the number of compound periods (20)
    Example: fv(1000, .0675, 20)
    """
    return a * (((1 + i) ** n - 1) / i)
