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Problem 193


Problem 193


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?


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?