C :

#include<stdio.h>

int main()
{
	int t,n,i;
	double a[30];
	a[0]=1;
	a[1]=3;
	for(i=2;i<30;i++)
		a[i]=a[i-1]+2*a[i-2];
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d",&n);
		printf("%.lf\n",a[n-1]);
	}
	return 0;
}

C++ :

#include<stdio.h>

int main()
{
	int t,n,i;
	double a[30];
	a[0]=1;
	a[1]=3;
	for(i=2;i<30;i++)
		a[i]=a[i-1]+2*a[i-2];
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d",&n);
		printf("%.lf\n",a[n-1]);
	}
	return 0;
}

Java :

import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		 int a=sc.nextInt();
		 int[] b=new int[31];
		 b[1]=1;
		 b[2]=3;
		 for(int i=3;i<31;i++){
			  b[i]=b[i-1]+2*b[i-2];  
		  }
		while(a--!=0){
		  System.out.println(b[sc.nextInt()]);
		}
	}
}

Python :

# coding=utf-8
def cg(x,y):
    r=1
    for c in range(x):
        r=r*(y-c)/(c+1)
    return int(r)
a=int(input())
for i in range(a):
    count=0
    b=int(input())
    for j in range(int(b/2+1)):
        count=count+cg(j,b-j)*(2**j)
    print(count)