Python脚本查找第n个质数 [英] Python script to find nth prime number

问题描述

我是Python的新手，我想我会尝试通过编写一个函数来找到第n个素数来学习一些技巧，但是我无法使我的代码正常工作.毫无疑问，这是由于我遗漏了一些基本知识，但是我很感谢您在发现错误之处方面的帮助！

I'm new to Python and I thought I'd try to learn the ropes a bit by writing a function to find the nth prime number, however I can't get my code to work properly. No doubt this is due to me missing something fundamental, but I'd appreciate your help in finding where it went wrong!

c=2
n=input("Which prime would you like? ")
n=int(n)
a=[]
l=len(a)

while l<=n:
    if c==2:
        a.append(c)
    elif (c % 2 ==0): #c is even
        break
    elif (c % 2 !=0): #c is odd
        if c<7:
            a.append(c)
        elif c >=7:
            for i in range(3,int((c+1)/2)):
                if (c % i ==0):
                    break
            else:
                a.append(c)
    else:            
        c+=1
a[n]

谢谢！ 安德鲁

推荐答案

这可以是一个开始.这将检查数字N是否可被2至int(sqrt(N)) + 1的所有数字整除，其中int函数将截断N的平方根.如果列表中的所有成员，python中的all()函数将返回True满足一些条件(此处不为零).您应该设置一个上限，因为对于很大的n来说这不是很有效.我把它留给你.

This can be a start. This checks whether the number N is divisible by all numbers from 2 to int(sqrt(N)) + 1, where the int function truncates the square root of N. The all() function in python returns True if all members of a list satisfy some condition (here not zero). You should set an upper bound as this is not very efficient for really large n. I'll leave that to you.

def nthprime(n):
    import math
    start = 2
    count = 0
    while True:
        if all([start % i for i in range(2, int(math.sqrt(start)) + 1)]) != 0:
            count += 1
            if count == n:
                return start
        start += 1 



In [91]: nthprime(50)
Out[91]: 229

In [92]: nthprime(100)
Out[92]: 541

使用此进行了测试.

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