C :

#include <stdio.h>
main()
{
	
	long long  a[35];
	int i,n;
	a[0]=2;
	while(scanf("%d",&n)!=EOF)
	{
		for(i=1;i<n;i++)
		{
			a[i]=3*a[i-1]+2;
		}
		printf("%lld\n",a[n-1]);
	}
	return 0;
 } 

C++ :

#include <iostream>
using namespace std;
int main(){
	long long a[35];
	a[0] = 2;
	for(int i=1;i<35;i++)
		a[i] = 3*a[i-1] + 2;
	for(int n;cin>>n;)
		cout<<a[n-1]<<endl;
	return 0;} 

Java :

public class Main{
	public static void main(String[] args) {   
		java.util.Scanner in=new java.util.Scanner(System.in);
		while(in.hasNext()) {
			int n=in.nextInt();
			long s=digui(n);
			System.out.println(s);
		}
}
	private static long digui(int n) {
			if(n<=0) {throw new IllegalArgumentException();}
		if(n==1)
			return 2;
		else
		return 3*digui(n-1)+2;
	}}