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Problem 800


Problem 800


Hybrid Integers

An integer of the form pqqp with prime numbers pq is called a hybrid-integer.
For example, 800=2552 is a hybrid-integer.

We define C(n) to be the number of hybrid-integers less than or equal to n.

You are given C(800)=2 and C(800800)=10790.

Find C(800800800800).


混合整数

若一个整数可以表示为pqqp的形式,且pq均为质数,则称其为混合整数
例如,800=2552是一个混合整数。

定义C(n)为小于等于n的所有混合整数的数目。

已知C(800)=2C(800800)=10790

C(800800800800)


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