[py] Project Euler

def isPrime(n):
    if n == 2:
        return True
    if n % 2 == 0:
        return False

    for i in range(3, int(n**0.5+1)):
        if n % i == 0:
            return False
        i+=2
    return True

def factorial(n):
    s = 1
    while(n > 0):
        s *= n
        n -= 1
    return s

def PE1(n):
    return sum(i for i in range(n) if i%3 == 0 or i%5 == 0)
#print PE1(1000)

def PE3(n):
    return max(i for i in xrange(1000000) if n%i == 0 and isPrime(i))
#print PE3(600851475143)

def PE6(n):
    return (sum(i for i in range(1, n+1))**2-sum(i*i for i in range(1, n+1)))
#print PE6(100)

def PE16(n):
    return sum(int(i) for i in str(n))
#print PE16(2**1000)

def PE20(n):
    return sum(int(i) for i in str(factorial(n)))
#print PE20(100)