Problem #347

Squarefree factorisations
Public 08/12/16 6xp Programming 55.6%

Consider the number $ 420 $

It can be decomposed in product of 2 squarefree factors in 4 different ways:
$ 2 \times 210 $
$ 6 \times 70 $
$ 10 \times 42 $
$ 14 \times 30 $

Let $ d(n) = \textrm{ number of pairs } (x,y) \textrm{ such as x,y squarefree, }x \times y = n \textrm{ and } x \le y $


Find $\displaystyle\sum_{k = 1}^{20,000,000} d(k) $

[My timing: 45 sec]



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