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Problem 193

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Squarefree Numbers

A positive integer n is called squarefree, if no square of a prime divides n, thus 1, 2, 3, 5, 6, 7, 10, 11 are squarefree, but not 4, 8, 9, 12.

How many squarefree numbers are there below 2⁵⁰?

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无平方因子数

若正整数n不能被任意素数的平方整除，则n被称为无平方因子数，因此1, 2, 3, 5, 6, 7, 10, 11是无平方因子的，而4, 8, 9, 12不是。

在小于2⁵⁰的数中，有多少个无平方因子数？

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