Maybe implement like this to be more readable?
```
from math import factorial

def comb(N, k):
    return factorial(N) / factorial(k) / factorial(N - k)
```

You chose this name because it is the same as `scipy.misc.comb`, right?
http://docs.scipy.org/doc/scipy/reference/generated/scipy.misc.comb.html
While it's nice having the same name for the same thing, I think it would be better to give a longer, more descriptive name here,
when I'm somewhere else and I see `comb` in the code I have to go look at the documentation to see what it means.