# Problem 530: GCD of Divisors
Every divisor d of a number n has a complementary divisor n/d. Let f(n)
be the sum of the greatest common divisor of d and n/d over all positive
divisors d of n, that is \$f(n)=\\displaystyle\\sum\\limits\_{d|n}\\,
\\text{gcd}(d,\\frac n d)\$. Let F be the summatory function of f, that
is \$F(k)=\\displaystyle\\sum\\limits\_{n=1}\^k \\, f(n)\$. You are
given that F(10)=32 and F(1000)=12776. Find F(1015).