杭电 hdu 2501

#include<iostream>
using namespace std;
#define N 40
long long a[N];
int main(){
    int n;
    cin>>n;
      
    a[0]=0;
    a[1]=1;
    a[2]=3;
    int i;
    for(i=3;i<N;++i)
        a[i]=a[i-1]+2*a[i-2];
    while(n--){
        int m;
        cin>>m;
        cout<<a[m]<<endl;
    }
    return 0;
}