尤拉計劃735:2n^2的因數

lt發表於2020-12-06

Let f(n) be the number of divisors of that are no greater than n. For example, f(n)=8, because there are 8 such divisors: 1,2,3,5,6,9,10,15. Note that 18 is also a divisor of 2*15^2, but it is not counted because it is greater than 15.

Let F(N)=∑f(n),n1->N. You are given F(15)=63, and F(1000)=15066 .

Find F(10^12).

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