Tetrahedron Cycles

Vamsi is standing at one vertex of a tetrahedron. He is quite active and he wouldn't stay idle. At each moment of time he makes a step from one vertex to another one along some edge of the tetrahedron.You can view more about Tetrahedron here Your task is to count the number of ways in which Vamsi can go from initial vertex and comeback to same vertex in exactly n steps. In other words, you are as