what is the flaw in my code
#include <bits/stdc++.h>
using namespace std;
#define ll long long int
#define mod 1000000007
#define mp make_pair
#define pb push_back
#define set(a) memset(a,0,sizeof(a))
#define sort(a) sort(a,a+n)
#define fo(i,n) for(i=0;i<n;i++)
#define PI 3.1415926535897932384626
int biker(int n)
{
if(n==1 or n==0)
return 1;
int ans=0;
ans=ans+biker(n-1)+(n-1)*biker(n-2);
return ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int t;
cin>>t;
while(t--)
{
int n;
cin>>n;
int ans=biker(n);
cout<<ans<<endl;
}
return 0;
}