Printing nth bell number
You can use the Dobinski formula for calculating Bell numbers more efficiently. 

Dobinski's formula is basically something like this line, although the actual implementation is a bit more complicated (this function neither returns precise value nor is efficient, see this blogpost for more on this):

import math
ITERATIONS = 1000
def bell_number(N):
    return (1/math.e) * sum([(k**N)/(math.factorial(k)) for k in range(ITERATIONS)])


E.g. you can use the mpmath package to calculate the nth Bell number using this formula:

from mpmath import *
mp.dps = 30
print bell(100)


You can check the implementation here