Everyone doesn't pass it to himself, and everyone has three ways to pass the ball, so the total number of passing ways for the nth time is the n power of 3.

There are three modes of transmission for the first time, and none of them will reach A; The second ***3*3=9 modes of transmission, of which 3 will reach A and 6 will not reach A; So it will infect A 6 species for the third time, and 3*3*3-6=2 1 species will not infect A; If 2 1 cases are transmitted to Party A for the fourth time, 3 * 3 * 3-2 1 = 60 cases will not be transmitted to Party A; For the fifth time, 60 situations were transmitted to Party A, but 3 * 3 * 3-60 =183 situations were not transmitted to Party A; There are 183 ways to send it back to A for the sixth time.