# Python calculating Catalan Numbers

In addition to xnx's answer, note that starting Python 3.8, with the addition of math.comb (binomial coefficient) in the standard library, we can also calculate Catalan numbers as such:

import math

def catalan(n):
return math.comb(2*n, n) / (n+1)

catalan(511) # 2.1902514917394773e+303


I assume you're using Python 3.

Your res /= (i + 1) should be res //= (i + 1) to force integer arithmetic:

def BinominalCoefficient(n,k):
res = 1
if (k > n - k):
k = n - k
for i in range(k):
res *= (n - i)
res //= (i + 1)
return res
def CatalanNumbers(n):
c = BinominalCoefficient(2*n, n)
return (c//(n+1))
print (CatalanNumbers(511))


returns

2190251491739477424254235019785597839694676372955883183976582551028726151813997871354391075304454574949251922785248583970189394756782256529178824038918189668852236486561863197470752363343641524451529091938039960955474280081989297135147411990495428867310575974835605457151854594468879961981363032236839645


You get nan because the divison /= in Python 3 returns a float which overflows to inf.