算法找到比最大素数小x [英] Algorithm to find largest prime number smaller than x

问题描述

我如何计算最大素数小于值x？

How do I calculate the largest prime number smaller than value x?

在实际事实上，它不必是精确的，只是近似的，靠近到x

In actual fact, it doesn't have to be exact, just approximate and close to x.

x是一个32位的整数。

x is a 32 bit integer.

的想法是，x是配置参数。我使用的最大素数小于X（称之为Y）作为参数传递给类构造函数。 y值必须是一个素数。

The idea is that x is a configuration parameter. I'm using the largest prime number less than x (call it y) as the parameter to a class constructor. The value y must be a prime number.

推荐答案

一些好的信息这里上的功能圆周率（x）的。显然，

Some good info here on the function pi(x). Apparently,

pi(x) = the number of primes less than x

和可以近似PI（X）与

and you can approximate pi(x) with

x/(log x - 1)

而

the n-th prime of that list of primes is equal to approximately n(log n)

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