组合数必定为整数

#include <iostream>
using namespace std;
typedef long long ll;
int main(){
    int n;  cin >> n;
    ll res = 1;
    for(ll i = 2 * n, k = 1; k <= n; i -- , k ++ )   res *= i, res /= (2 * n - i + 1);
    cout << res / (n + 1) << endl;
    return 0;
}

高精度的卡特兰数（高精度*高精度）可以查看此题：https://www.acwing.com/problem/content/132/