问题
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]
Thanks! Andrew
回答1:
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
Tested with this.
回答2:
Try like this?
print 2
for i in range(3,1000):
b = False
for j in range(2,i):
if i % j == 0:
b=True
if b == False:
print i
来源:https://stackoverflow.com/questions/48039350/python-script-to-find-nth-prime-number