P010.py

# -*- coding: utf-8 -*-
#===============================================================================
# The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
# Find the sum of all the primes below two million.
#===============================================================================
import math

def isPrime(n):
    '''check if integer n is a prime'''
    # make sure n is a positive integer
    n = abs(int(n))
    # 0 and 1 are not primes
    if n < 2:
        return False
    # 2 is the only even prime number
    if n == 2: 
        return True    
    # all other even numbers are not primes
    if not n & 1: 
        return False
    # range starts with 3 and only needs to go up the squareroot of n
    # for all odd numbers
    for x in range(3, int(math.sqrt(n))+1, 2):
        if n % x == 0:
            return False
    return True
    

pSum=0
for nn in range(2000000):
    if isPrime(nn):
        pSum += nn
#        print nn
        
print pSum
# 142913828922