求素数的第n个 [英] Finding the nth number of primes

问题描述

我不知道为什么这行不通.请帮助我

I can not figure out why this won't work. Please help me

from math import sqrt

pN = 0 
numPrimes = 0
num = 1

def checkPrime(x):
   '''Check\'s whether a number is a prime or not'''
   prime = True
   if(x==2):
      prime = True
   elif(x%2==0):
      prime=False
   else:
      root=int(sqrt(x))
      for i in range(3,root,2):
         if(x%i==0):
            prime=False
            break
   return prime

n = int(input("Find n number of primes. N being:"))

while( numPrimes != n ):
   if(  checkPrime( num ) == True ):
      numPrimes += 1
      pN = num
      print("{0}: {1}".format(numPrimes,pN))
   num += 1

print("Prime {0} is: {1}".format(n,pN))

推荐答案

您需要更改

root=int(sqrt(x))

进入

root=int(sqrt(x))+1

(例如，以9为例，int(sqrt(9))是3，而range(3, 3, 2)是[]，而您 do 确实想测试除以3！).

(Take 9 for instance, int(sqrt(9)) is 3, and range(3, 3, 2) is [], and you do really want to test dividing by 3!).

从技术上讲，1也不是质数.添加

Technically, 1 is not a prime either. Add

if(x<=1):
   prime = False

，您将得到与 http://www.rsok.com相同的结果/~jrm/first100primes.html

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