Number of possible Enigma machine combinations

enigma.py

# Number of possible starting configurations of an enigma machine
letters = 26
rotors_total = 5
rotors_machine = 3
cables = 10 # Must be < letters/2

def f(n): # Factorial
    s = 1;
    for i in xrange(2, n+1):
        s *= i
    return s

def choose(total, howmany): # Choose howmany elements from total elements
    return f(total)/(f(howmany)*f(total-howmany))

rotors = f(rotors_total)/f(rotors_machine-1) # choose of rotors
rotors *= letters**rotors_machine # Starting position

plugboard = 1
for i in xrange(0, cables):
    plugboard *= choose(letters - i*2, 2);
plugboard = plugboard/f(cables)

print(plugboard*rotors) # 158962555217826360000