Find nth prime number in python
By Purnendu DasHi, today we will learn about how to find an nth prime number in python. Finding a prime number is very easy in python. A prime number is a number which can only be divided by 1 and the number itself.
prime number
Python program to find nth prime number
Code :
n = int(input('Enter : '))
prime_numbers = [2,3]
i=3
if(0<n<3):
print(n,'th Prime Number is :',prime_numbers[n-1])
elif(n>2):
while (True):
i+=1
status = True
for j in range(2,int(i/2)+1):
if(i%j==0):
status = False
break
if(status==True):
prime_numbers.append(i)
if(len(prime_numbers)==n):
break
print(n,'th Prime Number is :', prime_numbers[n-1])
else:
print('Please Enter A Valid Number')
Output :
Explanation :
- At first, we take the input into the ‘n’ variable.
- We create a python list variable ‘prime_numbers’.
- Initially, we store 2,3 into the ‘prime_numbers’ variable.
- We create an ‘i’ variable. Initially, we store 3 into the ‘i’ variable.
- We create an if condition. If the value of n is greater than 0 and less than 3, it means if the value of n in between 1 to 2 then the operation will be performed. If the condition satisfied then print the list prime_numbers’s n-1 th position value.
- We create an elif condition. If the value is greater than 2 then the task is performed.
- We create an infinite While Loop. For storing the prime number into the ‘prime_numbers’ variable.
- increase the value of ‘i’ by one.
- We create a boolean variable ‘status’. Initially, it is ‘True’.
- We create a For Loop. The starting value of for loop variable ‘j’ is 2 and ending with (half+1) of the ‘i’ value. This for loop is used for checking the ‘i’ number is prime or not prime.
- If the remainder of (‘i’ value / ‘j’ value) is Zero then it not be a prime number. And break the for loop and ‘status‘ will be ‘False’.
- For all value of ‘j’, if the remainder not going to zero then the ‘status‘ will be ‘True’.
- We check if the status True then it is a prime number. And it stored into the ‘prime_numbers’.
- We check if the length of the list is equal to the ‘n’ value then the while loop will break.
- After breaking the while loop we print the nth prime number.
- We create an else section if the user types any wrong or negative value then program will print ‘Please Enter A Valid Number’.
In this whole process, we can easily find the nth prime number.
You may like to read :
- Catalan Number in Python – Iterative Approach (Factorial)
- Check whether two strings are anagram of each other using Python 3.x or earlier
Line 9: why not just use i+=2? It yields the same results.
not need to run upto i/2+1 we can run upto sqrt(i)+1
If not wanting to import math then you can do i**0.5 + 1. Certainly the program runs a lot quicker if not going up to i/2 + 1
I think we can do little easier than this:
def prime(n):
ls = []
if (0<n<3):
return n
else:
for i in range(2,n+1):
if n%i==0:
ls.append(i)
if (len(ls)==1) & (ls[0]==n):
return n
s = []
m = int(input('Enter : '))
i=0
while (len(s)!=m):
i+=1
if prime(i)!= None:
s.append(prime(i))
if len(s)==m:
print(s[-1])