def problem443():
    """


    Let g(n) be a sequence defined as follows:
       g(4) = 13,
       g(n) = g(n-1) + gcd(n, g(n-1)) for n > 4.

       The first few values are:

     n     4   5   6   7   8   9   10  11  12  13  14  15  16  17  18  19  20  ...
     g(n)  13  14  16  17  18  27  28  29  30  31  32  33  34  51  54  55  60  ...

       You are given that g(1 000) = 2524 and g(1 000 000) = 2624152.

       Find g(10^15).
    """

    pass
