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10-sumofprimes.py
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10-sumofprimes.py
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#find the sum of all primes below 2 million
import math
import time
past=time.time()
below_what=2000000
def isPrime(n):
if n==1:
return False
elif n<4:
return True
elif n%2 == 0:
return False
elif n<9:
return True
elif n%3 == 0:
return False
else:
r = int(math.sqrt(n)+1)
f=5
while f<=r:
if n%f == 0:
return False
if n%(f+2)== 0:
return False
f=f+6
return True
def sum_of_primes(n):
i= 1
som = 0
while i < n:
if isPrime(i):
som=som+i
i=i+1
if (i%1000==0):
print '.',
if(i%50000==0):
print
return som
print sum_of_primes(below_what)
present = time.time()
print "Runtime: " , present-past