{"app":{"locale":"en-GB"},"problem":{"content":"

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).

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