hdu-2501-Tiling_easy version

#include<stdio.h>
int a[31]={0,1,3};
int main()
{
int s,i;
scanf("%d",&s);
for(i=3;i<31;i++)
a[i]=a[i-1]+2*a[i-2];
while(s--)
{
int n;
scanf("%d",&n);
printf("%d\n",a[n]);
}
return 0;
}