Python: Print the number of prime numbers which are less than or equal to an given integer

Python Basic - 1: Exercise-38 with Solution

Write a Python program to print the number of prime numbers which are less than or equal to an given integer.

Input:
n (1 ≤ n ≤ 999,999)

Sample Solution:

Python Code:

primes = [1] * 500000
primes[0] = 0
 
for i in range(3, 1000, 2):
    if primes[i // 2]:
        primes[(i * i) // 2::i] = [0] * len(primes[(i * i) // 2::i])
 
print("Input the number(n):")
n=int(input())
if n < 4:
    print("Number of prime numbers which are less than or equal to n.:",n - 1)
else:
    print("Number of prime numbers which are less than or equal to n.:",sum(primes[:(n + 1) // 2]) + 1)

Sample Output:

Input the number(n):
 35
Number of prime numbers which are less than or equal to n.: 11

Pictorial Presentation:

Flowchart:

Python Code Editor:

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