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Problem 598


Problem 598


Split Divisibilities

Consider the number 48.
There are five pairs of integers $a$ and $b$ ($a \leq b$) such that $a \times b=48$: (1,48), (2,24), (3,16), (4,12) and (6,8).
It can be seen that both 6 and 8 have 4 divisors.
So of those five pairs one consists of two integers with the same number of divisors.

In general:
Let $C(n)$ be the number of pairs of positive integers $a \times b=n$, ($a \leq b$) such that $a$ and $b$ have the same number of divisors;
so $C(48)=1$.

You are given $C(10!)=3$: (1680, 2160), (1800, 2016) and (1890,1920).

Find $C(100!)$.


分配整除性

考虑数48。
有五对整数$a$和$b$($a \leq b$)满足$a \times b=48$:(1,48),(2,24),(3,16),(4,12)和(6,8)。
可以看出,6和8都有4个因数。
所以在这五对整数中,只有一对整数的因数数量相同。

一般地:
令$C(n)$表示所有满足$a \times b=n$($a \leq b$),且$a$和$b$的因数数量相同的正整数数对的数目;
因此已知$C(48)=1$。

此外,还已知$C(10!)=3$:(1680, 2160),(1800, 2016)和(1890,1920)。

求$C(100!)$。