Project Euler #12

euler12.py

from itertools import count
from itertools import dropwhile
from math import sqrt

def factorise(n):
    c = 0
    sr = int(sqrt(n))
    for i in range(1, sr + 1):
        if n % i == 0:
            c += 2
        if sr * sr == n:
            c -= 1
    return c

def triangle(n):
    return ((n + 1) * n) / 2

print dropwhile(lambda n: factorise(n) <= 500,
                    (triangle(i) for i in count())).next()